Thongchai Thailand

EARLY HOLOCENE SEA LEVEL RISE

Posted on: June 26, 2019

 

  1. An important component of climate change alarmism is that anthropogenic global warming (AGW) caused by fossil fuel emissions since the end of the Little Ice Age (LIA) will melt polar ice and cause catastrophic sea level rise. This scenario likely derives from paleo data about the prior interglacial, the Eemian, for which very violent sea level changes are recorded. Sea level rise of as much as 5 to 9 meters are reported and is generally attributed to a complete disintegration of the West Antarctic Ice Sheet (details in related post on the Eemian Interglacial [LINK] .
  2. Violent sea level rise events are also recorded in the current interglacial, the Holocene. They occurred as a series of “melt pulses” in the earlier part of this interglacial thousands of years ago. These melt pulses are described in some detail in the bibliography included below.
  3. The timing of these melt pulses is depicted graphically in the chart above. The timing indicates that violent sea level changes due to ice melt occurs in the initial breakdown of glaciation and not late in an interglacial.
  4. What we see in the bibliography below is that repeated but failed attempts to relate the melt pulses to polar ice sheets in Greenland and Antarctica. In the end the attribution of the melt pulses remain as non-polar ice sheets such as the Laurentide.
  5. It appears that the violent and catastrophic ice sheet melt events of the Holocene that caused the very low sea levels of the glacial maximum to rise to levels with which we are familiar, have already occurred for this interglacial cycle.
  6. Although the subsequent duration of the interglacial does show violent and chaotic cycles of cooling and warming (described in a related post [LINK] ), they do not include the kind of catastrophic changes in sea level seen in the early Holocene’s transition from glaciation.
  7. However, it remains an objective of climate science to find ways to describe the transition from the LIA to the current warm period in terms of early Holocene and early Eemian catastrophic sea level rise scenarios. These attempts have mostly failed except for rare events such as the collapse of the Larsen B Ice Shelf in 2002.
  8. Yet, as described in a related post [LINK] , localized events such as the collapse of the Larsen B ice shelf have more rational explanations in terms of geothermal heat. West Antarctica is geologically active and localized melt events are best described in those terms. An ice shelf collapse can cause temporary but possibly severe sea level rise because its source glacier flows faster to the sea in its absence  although, eventually it will construct a new ice shelf.
  9. In spite of the reality of Holocene sea level rise described above and in the bibliography below, climate science appears to be obsessed with the catastrophic sea level rise possibilities of melting polar ice. This fantasy of climate science is described in detail in a related post [LINK] .

 

[LIST OF POSTS ON THIS SITE]

 

 

EHSLR BIBLIOGRAPHY

  1. Ellison, Joanna C., and David R. Stoddart. “Mangrove ecosystem collapse during predicted sea-level rise: Holocene analogues and implications.” Journal of Coastal research(1991): 151-165.  Review of the stratigraphic record of mangrove ecosystems during sea- level changes of the Holocene shows that low islands will be particularly vulnerable to the loss of mangrove ecosystems during the rises of relative sea-level projected for the next 50 years. Mangrove ecosystems in these locations could keep up with a sea-level rise of up to 8-9 cm/100 years, but at rates of over 12 cm/100 years could not persist. This is due to low rates of sediment accumulation, with limited sources from outside the mangrove zone, such as from rivers or soil erosion sources. Other factors contributing to mangrove persistence are the primary production rate of forests, shoreline erosion due to deeper and more turbulent water and the frequency and intensity of tropical storms.
  2. Clark, Peter U., et al. “Origin of the first global meltwater pulse following the last glacial maximum.” Paleoceanography 11.5 (1996): 563-577.  Well‐dated sea level records show that the glacioeustatic rise following the last glacial maximum was characterized by two or possibly three brief intervals of rapid sea level rise separating periods with much lower rates. These very high rates of sea level rise indicate periods of exceptionally rapid deglaciation of remaining ice sheets. The Laurentide Ice Sheet is commonly targeted as the source of the first, and largest, of the meltwater pulses (mwp‐IA between ∼14,200 (12,200 14C years B.P.) and 13,700 years ago (11,700 14C years B.P.)). In all oceanic records of deglaciation of the former northern hemisphere ice sheets that we review, only those from the Gulf of Mexico and the Bermuda Rise show evidence of low δ18O values at the time of mwp‐IA, identifying the southern Laurentide Ice Sheet as a potential source for mwp‐IA. We question this source for mwp‐IA, however, because (1) ice sheet models suggest that this sector of the ice sheet contributed only a fraction (<10%) of the sea level needed for mwp‐IA, (2) melting this sector of the ice sheet at the necessary rate to explain mwp‐IA is physically implausible, and (3) ocean models predict a much stronger thermohaline response to the inferred freshwater pulse out of the Mississippi River into the North Atlantic than is recorded. This leaves the Antarctic Ice Sheet as the only other ice sheet capable of delivering enough sea level to explain mwp‐IA, but there are currently no well‐dated high‐resolution records to document this hypothesis. These conclusions suggest that reconstructions of the Laurentide Ice Sheet in the ICE‐4G model, which are constrained to match the sea level record, may be too low for time periods younger than 15,000 years ago. Furthermore, δ18O records from the Gulf of Mexico show variable fluxes of meltwater from the southern margin of the Laurentide Ice Sheet which can be traced to the opening and closing of eastward draining glacial‐lake outlets associated with surging ice sheet behavior. These variable fluxes through eastern outlets were apparently sufficient to affect formation of North Atlantic Deep Water, thus underscoring the sensitivity of this process to changes in freshwater forcing.
  3. Bard, Edouard, et al. “Deglacial sea-level record from Tahiti corals and the timing of global meltwater discharge.” Nature382.6588 (1996): 241.  The timing of the last deglaciation is important to our understanding of the dynamics of large ice sheets and their effects on the Earth’s surface. Moreover, the disappearance of the glacial ice sheets was responsible for dramatic increases in freshwater fluxes to the oceans, which probably disturbed the ocean’s thermohaline circulation and, hence, global climate. Sea-level increases bear witness to the melting of continental ice sheets, but only two such records—from Barbados and New Guinea corals—have been accurately dated. But these corals overlie active subduction zones, where tectonic movements are large and discontinuous (especially in New Guinea), so the apparent sea-level records may be contaminated by a complex tectonic component. Here we date fossil corals from Tahiti, which is far from plate boundaries (and thus is likely to be tectonically relatively stable) and remote from the locations of large former ice sheets. The resulting record indicates a large sea-level jump shortly before 13,800 calendar years BP, which corresponds to meltwater pulse 1A in the Barbados coral records8,9. The timing of this event is more accurately constrained in the Tahiti record, revealing that the meltwater pulse coincides with a short and intense climate cooling event12–15 that followed the initiation of the Bølling–Allerød warm period12–16, but preceded the Younger Dryas cold event by about 1,000 years.
  4. Josenhans, Heiner, et al. “Early humans and rapidly changing holocene sea levels in the queen Charlotte islands-Hecate strait, british Columbia, Canada.” Science 277.5322 (1997): 71-74.  Marine cores from the continental shelf edge of British Columbia (Canada) demonstrate that sea level at the shelf edge was 153 meters below present 14,000 calendar years ago and more than 30 meters lower than the maximum eustatic low of −120 meters. Dated artifacts, including stone tools, indicate that humans occupied this region by at least 10,200 calendar years before present (B.P.). Local sea level rose rapidly (5 centimeters per year) during the period of early human occupation as a result of eustatic sea-level rise and glacio-isostatic forebulge movement. This shelf edge site was first elevated and then subsided. The exposed shelf edge was available for human occupation and may have served as a migration route during times of lowered sea levels between 13,500 and 9500 14C years B.P.
  5. Toscano, Marguerite A., and Joyce Lundberg. “Early Holocene sea-level record from submerged fossil reefs on the southeast Florida margin.” Geology 26.3 (1998): 255-258.  Massive fossil (outlier) reefs are preserved seaward of the modern shelf and reef tract along the southeast Florida margin. Thermal ionization mass-spectrometric (TIMS) U-Th dating of 16 pristine Acropora palmata and head corals cored from two transects document early Holocene reef growth from 8.9 to 5.0 ka, from approximately −13.5 to −7 m MSL (mean sea level). These samples fill a gap in the Florida Keys sea-level database and clarify the timing of a significant decrease in the rate of sea-level rise. A portion of this interval, represented by a gap in the Caribbean record of A. palmata reefs, has been interpreted as reef drowning during an inferred catastrophic sea-level rise event of >45 mm/yr, or a 6.5 m rise between 7.6 and 7.2 ka, attributed to West Antarctic Ice Sheet instability and changes in marine ice extent between 8 and 7 ka. Continuous in situ shallow-water reef growth in Florida during this interval precludes the occurrence of exceedingly rapid rates of sea-level rise and is consistent with the North Atlantic record of deglaciation from 9 to 7 ka. Gaps in the early Holocene sea-level records for Florida and the Caribbean are thus more likely to be artifacts of limited sampling and/or core coverage, and not necessarily a result of drowning.
  6. Zheng, Yan, et al. “Intensification of the northeast Pacific oxygen minimum zone during the Bølling‐Allerød warm period.” Paleoceanography and Paleoclimatology 15.5 (2000): 528-536. Although climate records from several locations around the world show nearly synchronous and abrupt changes, the nature of the inferred teleconnection is still poorly understood. On the basis of preserved laminations and molybdenum enrichments in open margin sediments we demonstrate that the oxygen content of northeast Pacific waters at 800 rn depth during the B611ing-Aller6d warm period (15-13 kyr) was greatly reduced. Existing oxygen isotopic records of benthic and planktonic foraminifera suggest that this was probably due to suppressed ventilation at higher latitudes of the North Pacific. Comparison with ventilation records for the North Atlantic indicates an antiphased pattern of convection relative to the North Pacific over the past 22 kyr, perhaps due to variations in water vapor transport across Central America.
  7. Yu, Zicheng, and Ulrich Eicher. “Three amphi-Atlantic century-scale cold events during the Bølling-Allerød warm period.” Géographie physique et Quaternaire 55.2 (2001): 171-179.  Oxygen isotope composition of carbonates in the sediments of Crawford Lake, southern Canada, reveals multiple climatic events during the last deglaciation, including the Bølling warming, intra-Allerød cold period, Younger Dryas, Preboreal Oscillation, and early-Holocene 8.2-ka cooling. Here we present a high-resolution record (~50-yr sampling interval) of oxygen isotopes from this site during the Bølling-Allerød warm period and discuss its significance by comparing it with other records around the North Atlantic. These new data show three century-scale cold events, including the intra-Bølling cold period, Older Dryas, and intra-Allerød cold period. These climatic events correlate well in sequence and relative magnitude with those found in Greenland ice cores, European lacustrine sediments, and Atlantic Ocean sediments. Three similar oscillations in glaciochemical records from GISP2 ice core imply shift in atmospheric circulation patterns. The amphi-Atlantic distribution of these climate events suggests that these events likely originated from the North Atlantic Ocean and that climatic signals were transmitted through the atmosphere
  8. Clark, Peter U., et al. “Sea-level fingerprinting as a direct test for the source of global meltwater pulse IA.” Science 295.5564 (2002): 2438-2441.  The ice reservoir that served as the source for the meltwater pulse IA remains enigmatic and controversial. We show that each of the melting scenarios that have been proposed for the event produces a distinct variation, or fingerprint, in the global distribution of meltwater. We compare sea-level fingerprints associated with various melting scenarios to existing sea-level records from Barbados and the Sunda Shelf and conclude that the southern Laurentide Ice Sheet could not have been the sole source of the meltwater pulse, whereas a substantial contribution from the Antarctic Ice Sheet is consistent with these records.
  9. Kienast, Markus, et al. “Synchroneity of meltwater pulse 1a and the Bølling warming: new evidence from the South China Sea.” Geology 31.1 (2003): 67-70.  A twofold decrease in long-chain n-alcane (n-nonacosane) concentrations in a downcore record from the northern South China Sea indicates a rapid drop in the supply of terrigenous organic matter to the open South China Sea during the last deglaciation, paralleled by an equally rapid increase in sea-surface temperatures, corresponding with the Bølling warming at 14.7 ka. The sudden drop in terrigenous organic matter delivery to this marginal basin is interpreted to reflect a short-term response of local rivers to rapid sea-level rise, strongly implying that the Bølling warming and the onset of meltwater pulse (MWP) 1a are synchronous. This phase relation contrasts with the widely cited onset of this MWP 1a ca. 14 ka, and implies that previous studies postulating a weakening of deep-water formation in the North Atlantic due to massive meltwater discharge during MWP 1a need to be reevaluated.
  10. Weaver, Andrew J., et al. “Meltwater pulse 1A from Antarctica as a trigger of the Bølling-Allerød warm interval.” Science299.5613 (2003): 1709-1713.  Meltwater pulse 1A (MWP-1A) was a prominent feature of the last deglaciation. iT led to a sea-level rise of ∼20 meters ≈500 years. Concurrent with mwp-1A was the onset of the Bølling-Allerød interstadial event (14,600YBP), which marked the termination of the last glacial period. Previous studies have been unable to reconcile a warm Northern Hemisphere with mwp-1A originating from the Laurentide or Fennoscandian ice sheets. With the use of a climate model of intermediate complexity, we demonstrate that with mwp-1A originating from the Antarctic Ice Sheet, consistent with recent sea-level fingerprinting inferences, the strength of North Atlantic Deep Water (NADW) formation increases, thereby warming the North Atlantic region and providing an explanation for the onset of the Bølling-Allerød warm interval. The established mode of active NADW formation is then able to respond to subsequent freshwater forcing from the Laurentide and Fennoscandian ice sheets, setting the stage for the Younger Dryas cold period.
  11. Webster, Jody M., et al. “Drowning of the− 150 m reef off Hawaii: a casualty of global meltwater pulse 1A?.” Geology32.3 (2004): 249-252.  We present evidence that the drowning of the −150 m coral reef around Hawaii was caused by rapid sea-level rise associated with meltwater pulse 1A (MWP-1A) during the last deglaciation. New U/Th and 14C accelerator mass spectrometry dates, combined with reinterpretation of existing radiometric dates, constrain the age of the coral reef to 15.2–14.7 ka (U/Th age), indicating that reef growth persisted for 4.3 k.y. following the end of the Last Glacial Maximum at 19 ka. The drowning age of the reef is roughly synchronous with the onset of MWP-1A between 14.7 and 14.2 ka. Dates from coralline algal material range from 14 to 10 cal ka (calibrated radiocarbon age), 1–4 k.y. younger than the coral ages. A paleoenvironmental reconstruction incorporating all available radiometric dates, high-resolution bathymetry, dive observations, and coralgal paleobathymetry data indicates a dramatic rise in sea level around Hawaii ca. 14.7 ka. Paleowater depths over the reef crest increased rapidly above a critical depth (30–40 m), drowning the shallow reef-building Porites corals and causing a shift to deep-water coralline algal growth, preserved as a crust on the drowned reef crest.
  12. Peltier, W. R. “On the hemispheric origins of meltwater pulse 1a.” Quaternary Science Reviews 24.14-15 (2005): 1655-1671. During the glacial–interglacial transition that began subsequent to the Last Glacial Maximum approximately 21,000 calendar years ago, globally averaged (eustatic) sea-level rose by approximately 120 m as climate warmed to its current (Holocene) state. This rise of relative sea-level (RSL) did not occur smoothly, however, but was characterized by the occurrence of one or more episodes of extremely rapid increase. The most extreme of these events has come to be referred to as meltwater pulse 1a, and was initially identified in the coral based record of RSL history from the island of Barbados in the Caribbean Sea. Although it has usually been assumed that this episode of rapid RSL rise was derivative of a partial collapse of the northern hemisphere ice sheets, it has recently been suggested that this pulse could have originated in a dramatic melt-back of the Antarctic Ice Sheet. In this paper the arguments presented in favour of the southern hemisphere source are revisited in order to assess the plausibility of this Antarctic scenario. Based upon the analyses presented, it is concluded that the evidence previously provided in support of the southern hemisphere scenario is in fact unable to rule out an entirely northern hemisphere source for the meltwater pulse 1a. Since explicit evidence does exist that both the Laurentide and Fennoscandian ice sheets contributed to this event and that Antarctic ice sheet melting occurred significantly later, the southern hemisphere appears not to have been a prime mover of northern hemisphere events.
  13. Hill, T. M., et al. “Pre-Bølling warming in Santa Barbara Basin, California: surface and intermediate water records of early deglacial warmth.” Quaternary Science Reviews 25.21-22 (2006): 2835-2845.  A new piston core from Santa Barbara Basin, California provides evidence of the timing, magnitude, and character of deglaciation, including evidence of warming prior to Termination IA. IMAGES Site MD02-2503 (570 m water depth) consists of intermittently laminated hemipelagic sediments extending to Interstadial (D/O) event 6 (∼34 ka), that accumulated at ∼135 cm/ka. During the deglacial episode (16.75–10 ka)δ18O values decreased by 3.2‰ in the planktonic species Globigerina bulloides, indicating a total warming of 8–9 °C recorded by surface-dwelling foraminifera (inferred by removing the 1‰ influence of ice volume change). Similarly, benthic species (Bolivina argentea and Uvigerina peregrina) record a 1.65‰ δ18O decrease across the deglacial, interpreted as a 2–3 °C warming at upper intermediate depthsδ18O values of both planktonic and benthics indicate that surface and intermediate waters began to warm ∼2 ka prior to Termination IA, beginning at ∼16.5 ka. Intermediate water warming exhibits similar structure and synchronous timing with surface waters. These findings are consistent with a growing number of records from around the globe that exhibit pre-Bølling warming prior to Termination IA, and extends the record of such processes to the northern Pacific.
  14. Bondevik, Stein, et al. “Changes in North Atlantic radiocarbon reservoir ages during the Allerød and Younger Dryas.” Science 312.5779 (2006): 1514-1517. Estimates of the radiocarbon age of seawater are required in correlations between marine and terrestrial records of the late Quaternary climate. We radiocarbon-dated marine shells and terrestrial plant remains deposited in two bays on Norway’s west coast between 11,000 and 14,000 years ago, a time of large and abrupt climatic changes that included the Younger Dryas (YD) cold episode. The radiocarbon age difference between the shells and the plants showed that sea surface reservoir ages increased from 400 to 600 years in the early YD, stabilized for 900 years, and dropped by 300 years within a century across the YD-Holocene transition.
  15. Stanford, Jennifer D., et al. “Timing of meltwater pulse 1a and climate responses to meltwater injections.” Paleoceanography21.4 (2006).  The temporal relationship between meltwater pulse 1a (mwp‐1a) and the climate history of the last deglaciation remains a subject of debate. By combining the Greenland Ice Core Project δ18O ice core record on the new Greenland ice core chronology 2005 timescale with the U/Th‐dated Barbados coral record, we conclusively derive that mwp‐1a did not coincide with the sharp Bølling warming but instead with the abrupt cooling of the Older Dryas. To evaluate whether there is a relationship between meltwater injections, North Atlantic Deep Water (NADW) formation, and climate change, we present a high‐resolution record of NADW flow intensity from Eirik Drift through the last deglaciation. It indicates only a relatively minor 200‐year weakening of NADW flow, coincident with mwp‐1a. Our compilation of records also indicates that during Heinrich event 1 and the Younger Dryas there were no discernible sea level rises, and yet these periods were characterized by intense NADW slowdowns/shutdowns. Clearly, deepwater formation and climate are not simply controlled by the magnitude or rate of meltwater addition. Instead, our results emphasize that the location of meltwater pulses may be more important, with NADW formation being particularly sensitive to surface freshening in the Arctic/Nordic Seas.
  16. Bird, Michael I., et al. “An inflection in the rate of early mid-Holocene eustatic sea-level rise: A new sea-level curve from Singapore.” Estuarine, Coastal and Shelf Science 71.3-4 (2007): 523-536. This study presents a sea-level curve from ∼9500 to ∼6500 cal BP for the farfield location of Singapore, on the Sunda Shelf in southeast Asia. The curve is based on more than 50 radiocarbon dates from elevations of +1.43 m to −15.09 m representing sea-level index points in intertidal mangrove and shallow marine sediments deposited by sea-level riseaccompanying deglaciation. The results indicate that mean sea level rose rapidly from around −17 m at 9500 cal BP to around −3 m by 8000 cal BP. After this time, the data suggest (but do not unequivocally prove) that the rate of sea-rise slowed for a period of 300–500 years centred on ∼7700 cal BP, shortly after the cessation of meltwater input to the oceans from the northern hemisphere. Renewed sea-level rise amounting to 3–5 m began around 7400 cal BP and was complete by 7000 cal BP. The existence of an inflection in the rate of sea-level rise, with a slow-down centred on ∼7700 cal BP, is broadly consistent with other available sea-level curves over this interval and is supported by evidence of stable shorelines and delta initiation elsewhere at this time, as well as evidence of comparatively rapid retreat of the West Antarctic ice sheet beginning around 7500 cal BP. ‘Stepped’ sea-level rise occurring shortly after 7500 cal BP and also earlier during deglaciation may have served to focus significant post-glacial episodes of human maritime/coastal dispersal, into comparatively narrow time intervals.
    • Hori, Kazuaki, and Yoshiki Saito. “An early Holocene sea‐level jump and delta initiation.” Geophysical Research Letters 34.18 (2007).  Early Holocene sea‐level change controlled the evolution of clastic coastal depositional systems. Radiocarbon‐dated borehole cores obtained from three incised‐valley‐fill systems in Asia (Changjiang, Song Hong, and Kiso River) record very similar depositional histories, especially between about 9000 and 8500 cal BP. Sedimentary facies changes from estuarine sand and mud to shelf or prodelta mud suggest that the marine influence in the incised valleys increased during this period. In addition, large decreases in sediment accumulation rates occurred. A sea‐level jump causes an estuarine system and its depocenter to move rapidly landward. It is possible that the final collapse of the Laurentide Ice Sheet, accompanied by catastrophic drainage of glacial lakes, at approximately 8500 cal BP caused such a jump. The jump was followed immediately by a period of decelerated sea‐level rise that promoted delta initiation.
    • Turney, Chris SM, and Heidi Brown. “Catastrophic early Holocene sea level rise, human migration and the Neolithic transition in Europe.” Quaternary Science Reviews 26.17-18 (2007): 2036-2041.  The collapse of the Laurentide Ice Sheet and release of freshwater 8740–8160 years ago abruptly raised global sea levels by up to 1.4 m. The effect on human populations is largely unknown. Here we constrain the time of the main sea level rise and investigate its effect on the onset of the Neolithic across Europe. An analysis of radiocarbon ages and palaeoshoreline reconstruction supports the hypothesis that flooding of coastal areas led to the sudden loss of land favoured by early farmers and initiated an abrupt expansion of activity across Europe, driven by migrating Neolithic peoples.
    • Asami, Ryuji, et al. “Evidence for tropical South Pacific climate change during the Younger Dryas and the Bølling–Allerød from geochemical records of fossil Tahiti corals.” Earth and Planetary Science Letters 288.1-2 (2009): 96-107. We present monthly resolved records of strontium/calcium (Sr/Ca) and oxygen isotope (δ18O) ratios from well-preserved fossil corals drilled during the Integrated Ocean Drilling Program (IODP) Expedition 310 “Tahiti Sea Level” and reconstruct sea surface conditions in the central tropical South Pacific Ocean during two time windows of the last deglaciation. The two Tahiti corals examined here are uranium/thorium (U/Th)-dated at 12.4 and 14.2 ka, which correspond to the Younger Dryas (YD) cold reversal and the Bølling–Allerød (B–A) warming of the Northern Hemisphere, respectively. The coral Sr/Ca records indicate that annual average sea surface temperature (SST) was 2.6–3.1 °C lower at 12.4 ka and 1.0–1.6 °C lower at 14.2 ka relative to the present, with no significant changes in the amplitude of the seasonal SST cycle. These cooler conditions were accompanied by seawater δ18O (δ18Osw) values higher by ~ 0.8‰ and ~ 0.6‰ relative to the present at 12.4 and 14.2 ka, respectively, implying more saline conditions in the surface waters. Along with previously published coral Sr/Ca records from the island [Cohen and Hart (2004), Deglacial sea surface temperatures of the western tropical Pacific: A new look at old coral. Paleoceanography 19, PA4031, doi:10.1029/2004PA001084], our new Tahiti coral records suggest that a shift toward lower SST by ~ 1.5 °C occurred from 13.1 to 12.4 ka, which was probably associated with a shift toward higher δ18Osw by ~ 0.2‰. Along with a previously published coral Sr/Ca record from Vanuatu [Corrège et al. (2004), Interdecadal variation in the extent of South Pacific tropical waters during the Younger Dyras event. Nature 428, 927–929], the Tahiti coral records provide new evidence for a pronounced cooling of the western to central tropical South Pacific during the Northern Hemisphere YD event.
      • Liu, Zhengyu, et al. “Transient simulation of last deglaciation with a new mechanism for Bølling-Allerød warming.” Science325.5938 (2009): 310-314.  We conducted the first synchronously coupled atmosphere-ocean general circulation model simulation from the Last Glacial Maximum to the Bølling-Allerød (BA) warming. Our model reproduces several major features of the deglacial climate evolution, suggesting a good agreement in climate sensitivity between the model and observations. In particular, our model simulates the abrupt BA warming as a transient response of the Atlantic meridional overturning circulation (AMOC) to a sudden termination of freshwater discharge to the North Atlantic before the BA. In contrast to previous mechanisms that invoke AMOC multiple equilibrium and Southern Hemisphere climate forcing, we propose that the BA transition is caused by the superposition of climatic responses to the transient CO2 forcing, the AMOC recovery from Heinrich Event 1, and an AMOC overshoot.
      • Griffiths, Michael L., et al. “Increasing Australian–Indonesian monsoon rainfall linked to early Holocene sea-level rise.” Nature Geoscience 2.9 (2009): 636.  The Australian–Indonesian summer monsoon affects rainfall variability and hence terrestrial productivity in the densely populated tropical Indo–Pacific region. It has been proposed that the main control of summer monsoon precipitation on millennial timescales is local insolation1,2,3, but unravelling the mechanisms that have influenced monsoon variability and teleconnections has proven difficult, owing to the lack of high-resolution records of past monsoon behaviour. Here we present a precisely dated reconstruction of monsoon rainfall over the past 12,000 years, based on oxygen isotope measurements from two stalagmites collected in southeast Indonesia. We show that the summer monsoon precipitation increased during the Younger Dryas cooling event, when Atlantic meridional overturning circulation was relatively weak4. Monsoon precipitation intensified even more rapidly from 11,000 to 7,000 years ago, when the Indonesian continental shelf was flooded by global sea-level rise5,6,7. We suggest that the intensification during the Younger Dryas cooling was caused by enhanced winter monsoon outflow from Asia and a related southward migration of the intertropical convergence zone8. However, the early Holocene intensification of monsoon precipitation was driven by sea-level rise, which increased the supply of moisture to the Indonesian archipelago.
      • Bard, Edouard, Bruno Hamelin, and Doriane Delanghe-Sabatier. “Deglacial meltwater pulse 1B and Younger Dryas sea levels revisited with boreholes at Tahiti.” Science327.5970 (2010): 1235-1237.  Reconstructing sea-level changes during the last deglaciation provides a way of understanding the ice dynamics that can perturb large continental ice sheets. The resolution of the few sea-level records covering the critical time interval between 14,000 and 9,000 CYBP calendar years before the present is still insufficient to draw conclusions about sea-level changes associated with the Younger Dryas cold event and the meltwater pulse 1B (MWP-1B). We used the uranium-thorium method to date shallow-living corals from three new cores drilled onshore in the Tahiti barrier reef. No significant discontinuity can be detected in the sea-level rise during the MWP-1B period. The new Tahiti sea-level record shows that the sea-level rise slowed down during the Younger Dryas before accelerating again during the Holocene.
      • Bird, Michael I., et al. “Punctuated eustatic sea-level rise in the early mid-Holocene.” Geology 38.9 (2010): 803-806.  Whether eustatic sea-level rise through the Holocene has been punctuated or continuous has remained controversial for almost two decades. Resolving this debate has implications for predicting future responses of remaining ice sheets to climate change and also for understanding the drivers of human settlement and dispersal patterns through prehistory. Here we present a sea-level curve for the past 8900 yr from Singapore, a tectonically stable location remote from ice-loading effects. We also present critical and unique sedimentation rate, organic δ13C, and foraminiferal δ13C proxy records of sea-level change derived from a shallow-marine sediment core from the same area over the same time interval. The sea-level curve, corroborated by the independent proxy records, suggests rapid rise at a rate of 1.8 m/100 yr until 8100 cal (calibrated) yr B.P., a near cessation in the rate of sea-level rise between 7800 and 7400 cal yr B.P., followed by a renewed rise of 4–5 m that was complete by 6500 cal yr B.P. We suggest that this period of relatively stable sea level during the early to mid-Holocene enabled modern deltas to advance, providing a highly productive environment for the establishment of coastal sedentary agriculture. Periods of rapid sea-level rise before and after may have catalyzed significant postglacial episodes of human dispersal in coastal regions.
      • Obbink, Elizabeth A., Anders E. Carlson, and Gary P. Klinkhammer. “Eastern North American freshwater discharge during the Bølling-Allerød warm periods.” Geology 38.2 (2010): 171-174. During the last deglaciation (ca. 19–6.5 ka), increased freshwater discharge to the North Atlantic likely caused reductions in Atlantic meridional overturning circulation (AMOC) strength. However, the locations and rates of freshwater discharge are not well constrained, particularly those during the centennial-scale climate oscillations of the Bølling-Allerød warm periods (ca. 14.6–12.9 ka). Here we reconstruct the salinity-dependent δ18Osw (sw, seawater) adjacent to the eastern outlets of North America, using paired Mg/Ca and δ18O records on planktonic foraminifera, to investigate whether increased discharge to the North Atlantic caused reductions in AMOC during the Bølling-Allerød and earlier periods of deglaciation. In general, δ18Osw decreased and inferred freshwater discharge increased during periods of reduced AMOC. During the Bølling-Allerød, δ18Osw decreases coincided with three reductions in AMOC strength ca. 14.1, 13.8, and 13.3 ka. Freshwater discharge modeling suggests that discharge increases of 0.03–0.05 Sverdrups (106 m3 s−1) would explain these δ18Osw decreases, which were sufficient to force reductions in AMOC strength. Concurrent changes in North Atlantic temperature, and subtropical and tropical atmospheric circulation and precipitation imply that small variations in the North Atlantic hydrologic system may have significant impacts on Northern Hemisphere climate.
      • Smith, D. E., et al. “The early Holocene sea level rise.” Quaternary Science Reviews 30.15-16 (2011): 1846-1860.  The causes, anatomy and consequences of the early Holocene sea level rise (EHSLR) are reviewed. The rise, of ca 60m, took place over most of the Earth as the volume of the oceans increased during deglaciation and is dated at 11,650–7000 cal. BP. The EHSLR was largely driven by meltwater release from decaying ice masses and the break up of coastal ice streams. The patterns of ice sheet decay and the evidence for meltwater pulses are reviewed, and it is argued that the EHSLR was a factor in the ca 8470 BP flood from Lake Agassiz-Ojibway. Patterns of relative sea level changes are examined and it is argued that in addition to regional variations, temporal changes are indicated. The impact of the EHSLR on climate is reviewed and it is maintained that the event was a factor in the 8200 BP cooling event, as well as in changes in ocean current patterns and their resultant effects. The EHSLR may also have enhanced volcanic activity, but no clear evidence of a causal link with submarine sliding on continental slopes and shelves can yet be demonstrated. The rise probably influenced rates and patterns of human migrations and cultural changes. It is concluded that the EHSLR was a major event of global significance, knowledge of which is relevant to an understanding of the impacts of global climate change in the future.
      • Deschamps, Pierre, et al. “Ice-sheet collapse and sea-level rise at the Bølling warming 14,600 years ago.” Nature483.7391 (2012): 559.  Past sea-level records provide invaluable information about the response of ice sheets to climate forcing. Some such records suggest that the last deglaciation was punctuated by a dramatic period of sea-level rise, of about 20 metres, in less than 500 years. Controversy about the amplitude and timing of this meltwater pulse (MWP-1A) has, however, led to uncertainty about the source of the melt water and its temporal and causal relationships with the abrupt climate changes of the deglaciation. Here we show that MWP-1A started no earlier than 14,650 years ago and ended before 14,310 years ago, making it coeval with the Bølling warming. Our results, based on corals drilled offshore from Tahiti during Integrated Ocean Drilling Project Expedition 310, reveal that the increase in sea level at Tahiti was between 12 and 22 metres, with a most probable value between 14 and 18 metres, establishing a significant meltwater contribution from the Southern Hemisphere. This implies that the rate of eustatic sea-level rise exceeded 40 millimetres per year during MWP-1A.
      • Törnqvist, Torbjörn E., and Marc P. Hijma. “Links between early Holocene ice-sheet decay, sea-level rise and abrupt climate change.” Nature Geoscience 5.9 (2012): 601.  The beginning of the current interglacial period, the Holocene epoch, was a critical part of the transition from glacial to interglacial climate conditions. This period, between about 12,000 and 7,000 years ago, was marked by the continued retreat of the ice sheets that had expanded through polar and temperate regions during the preceding glacial. This meltdown led to a dramatic rise in sea level, punctuated by short-lived jumps associated with catastrophic ice-sheet collapses. Tracking down which ice sheet produced specific sea-level jumps has been challenging, but two events between 8,500 and 8,200 years ago have been linked to the final drainage of glacial Lake Agassiz in north-central North America. The release of the water from this ice-dammed lake into the ocean is recorded by sea-level jumps in the Mississippi and Rhine-Meuse deltas of approximately 0.4 and 2.1 metres, respectively. These sea-level jumps can be related to an abrupt cooling in the Northern Hemisphere known as the 8.2 kyr event, and it has been suggested that the freshwater release from Lake Agassiz into the North Atlantic was sufficient to perturb the North Atlantic meridional overturning circulation. As sea-level rise on the order of decimetres to metres can now be detected with confidence and linked to climate records, it is becoming apparent that abrupt climate change during the early Holocene associated with perturbations in North Atlantic circulation required sustained freshwater release into the ocean.
      • Golledge, N. R., et al. “Antarctic contribution to meltwater pulse 1A from reduced Southern Ocean overturning.” Nature Communications 5 (2014): 5107.  During the last glacial termination, the upwelling strength of the southern polar limb of the Atlantic Meridional Overturning Circulation varied, changing the ventilation and stratification of the high-latitude Southern Ocean. During the same period, at least two phases of abrupt global sea-level rise—meltwater pulses—took place. Although the timing and magnitude of these events have become better constrained, a causal link between ocean stratification, the meltwater pulses and accelerated ice loss from Antarctica has not been proven. Here we simulate Antarctic ice sheet evolution over the last 25 kyr using a data-constrained ice-sheet model forced by changes in Southern Ocean temperature from an Earth system model. Results reveal several episodes of accelerated ice-sheet recession, the largest being coincident with meltwater pulse 1A. This resulted from reduced Southern Ocean overturning following Heinrich Event 1, when warmer subsurface water thermally eroded grounded marine-based ice and instigated a positive feedback that further accelerated ice-sheet retreat.
      • Thiagarajan, Nivedita, et al. “Abrupt pre-Bølling–Allerød warming and circulation changes in the deep ocean.” Nature511.7507 (2014): 75.  Several large and rapid changes in atmospheric temperature and the partial pressure of carbon dioxide in the atmosphere probably linked to changes in deep ocean circulation occurred during the last deglaciation. The abrupt temperature rise in the Northern Hemisphere and the restart of the Atlantic meridional overturning circulation at the start of the Bølling–Allerød interstadial, 14,700 years ago, are among the most dramatic deglacial events, but their underlying physical causes are not known. Here we show that the release of heat from warm waters in the deep North Atlantic Ocean probably triggered the Bølling–Allerød warming and reinvigoration of the Atlantic meridional overturning circulation. Our results are based on coupled radiocarbon and uranium-series dates, along with clumped isotope temperature estimates, from water column profiles of fossil deep-sea corals in a limited area of the western North Atlantic. We find that during Heinrich stadial 1 (the cool period immediately before the Bølling–Allerød interstadial), the deep ocean was about three degrees Celsius warmer than shallower waters above. This reversal of the ocean’s usual thermal stratification pre-dates the Bølling–Allerød warming and must have been associated with increased salinity at depth to preserve the static stability of the water column. The depleted radiocarbon content of the warm and salty water mass implies a long-term disconnect from rapid surface exchanges, and, although uncertainties remain, is most consistent with a Southern Ocean source. The Heinrich stadial 1 ocean profile is distinct from the modern water column, that for the Last Glacial Maximum and that for the Younger Dryas, suggesting that the patterns we observe are a unique features of the deglacial climate system. Our observations indicate that the deep ocean influenced dramatic Northern Hemisphere warming by storing heat at depth that preconditioned the system for a subsequent abrupt overturning event during the Bølling–Allerød interstadial.

       

       

      CHANELED SCABLAND

       

      MISSOULA FLOODS BIBLIOGRAPHY 

      1. Bretz, J. Harlen. “The Lake Missoula floods and the channeled scabland.” The Journal of Geology 77.5 (1969): 505-543.  This paper reviews the outstanding evidence for (1) repeated catastrophic outbursts of Montana’s glacially dammed Lake Missoula, (2) consequent overwhelming in many places of the preglacial divide along the northern margin of the Columbia Plateau in Washington, (3) remaking of the plateau’s preglacial drainage pattern into an anastomosing complex of floodwater channels (Channeled Scabland) locally eroded hundreds of feet into underlying basalt, (4) convergence of these flood-born rivers into the Columbia Valley at least as far as Portland, Oregon, and (5) deposition of a huge delta at Portland. Evidence that the major scabland rivers and the flooded Columbia were hundreds of feet deep exists in (1) gravel and boulder bars more than 100 feet high in mid-channels, (2) subfluvial cataract cliffs, alcoves, and plunge pools hundreds of feet in vertical dimension, (3) back-flooded silts high on slopes of preglacial valleys tributary to the scabland complex, and (4) the delta at Portland. Climatic oscillations of the Cordilleran ice sheet produced a succession of Lake Missoulas. Following studies by the writer, later investigators have correlated the Montana glacial record with recurrent scabland floods by soil profiles and a glacial and loessial stratigraphy, and have approximately dated some events by volcanic ash layers, peat deposits, and an archaeological site. Several unsolved problems are outlined in this paper.
      2. Baker, Victor R., and Daniel J. Milton. “Erosion by catastrophic floods on Mars and Earth.” Icarus 23.1 (1974): 27-41.  The large Martian channels, especially Kasei, Ares, Tiu, Simud, and Mangala Valles, show morphologic features strikingly similar to those of the Channeled Scabland of eastern Washington, produced by the catastrophic breakout floods of Pleistocene Lake Missoula. Features in the overall pattern include the great size, regional anastomosis, and low sinuosity of the channels. Erosional features are streamlined hills, longitudinal grooves, inner channel cataracts, scour upstream of flow obstacles, and perhaps marginal cataracts and butte and basin topography. Depositional features are bar complexes in expanding reaches and perhaps pendant bars and alcove bars. Scabland erosion takes place in exceedingly deep, swift floodwater acting on closely jointed bedrock as a hydrodynamic consequence of secondary flow phenomena, including various forms of macroturbulent votices and flow separations. If the analogy to the Channeled Scabland is correct, floods involving water discharges of millions of cubic meters per second and peak flow velocities of tens of meters per second, but perhaps lasting no more than a few days, have occurred on Mars.
      3. Atwater, Brian F. “Periodic floods from glacial Lake Missoula into the Sanpoil arm of glacial Lake Columbia, northeastern Washington.” Geology 12.8 (1984): 464-467. At least 15 floods ascended the Sanpoil arm of glacial Lake Columbia during a single glaciation. Varves between 14 of the flood beds indicate one back-flooding every 35 to 55 yr. This regularity suggests that the floods came from an ice-dammed lake that was self-dumping. Probably the self-dumping lake was glacial Lake Missoula, Montana, because the floods accord with inferred emptyings of that lake in frequency and number, apparently entered Lake Columbia from the east, and produced beds resembling backflood deposits of Lake Missoula floods in southern Washington.
      4. Clarke, G. K. C., W. H. Mathews, and Robert T. Pack. “Outburst floods from glacial Lake Missoula.” Quaternary Research 22.3 (1984): 289-299. The Pleistocene outburst floods from glacial Lake Missoula, known as the “Spokane Floods”, released as much as 2184 km3 of water and produced the greatest known floods of the geologic past. A computer simulation model for these floods that is based on physical equations governing the enlargement by water flow of the tunnel penetrating the ice dam is described. The predicted maximum flood discharge lies in the range 2.74 × 106−13.7 × 106 m3 sec−1, lending independent glaciological support to paleohydrologic estimates of maximum discharge.
      5. Waitt Jr, Richard B. “Case for periodic, colossal jokulhlaups from Pleistocene glacial Lake Missoula.” Geological Society of America Bulletin 96.10 (1985): 1271-1286. Two classes of field evidence firmly establish that late Wisconsin glacial Lake Missoula drained periodically as scores of colossal jökulhlaups (glacier-outburst floods). (1) More than 40 successive, flood-laid, sand-to-silt graded rhythmites accumulated in back-flooded valleys in southern Washington. Hiatuses are indicated between flood-laid rhythmites by loess and volcanic ash beds. Disconformities and nonflood sediment between rhythmites are generally scant because precipitation was modest, slopes gentle, and time between floods short. (2) In several newly analyzed deposits of Pleistocene glacial lakes in northern Idaho and Washington, lake beds comprising 20 to 55 varves (average = 30–40) overlie each successive bed of Missoula-flood sediment. These and many other lines of evidence are hostile to the notion that any two successive major rhythmites were deposited by one flood; they dispel the notion that the prodigious floods numbered only a few. The only outlet of the 2,500-km3 glacial Lake Missoula was through its great ice dam, and so the dam became incipiently buoyant before the lake could rise enough to spill over or around it. Like Grímsvötn, Iceland, Lake Missoula remained sealed as long as any segment of the glacial dam remained grounded; when the lake rose to a critical level ∼600 m in depth, the glacier bed at the seal became buoyant, initiating underflow from the lake. Subglacial tunnels then grew exponentially, leading to catastrophic discharge. Calculations of the water budget for the lake basin (including input from the Cordilleran ice sheet) suggest that the lakes filled every three to seven decades. The hydrostatic prerequisites for a jökulhlaup were thus re-established scores of times during the 2,000- to 2,500-yr episode of last-glacial damming. J Harlen Bretz’s “Spokane flood” outraged geologists six decades ago, partly because it seemed to flaunt catastrophism. The concept that Lake Missoula discharged regularly as jökulhlaups now accords Bretz’s catastrophe with uniformitarian principles.
      6. Baker, Victor R., and Russell C. Bunker. “Cataclysmic late Pleistocene flooding from glacial Lake Missoula: A review.” Quaternary Science Reviews 4.1 (1985): 1-41.Late Wisconsin floods from glacial Lake Missoula occurred between approximately 16 and 12 ka BP. Many floods occurred; some were demonstrably cataclysmic. Early studies of Missoula flooding centered on the anomalous physiography of the Channeled Scabland, which J. Harlen Bretz hypothesized in 1923 to have developed during a debacle that he named ‘The Spokane Flood’. Among the ironies in the controversy over this hypothesis was a mistaken view of uniformitarianism held by Bretz’s adversaries. After resolution of the scabland’s origin by cataclysmic outburst flooding from glacial Lake Missoula, research since 1960 emphasized details of flood magnitudes, frequency, routing and number. Studies of flood hydraulics and other physical parameters need to utilize modern computerized procedures for flow modeling, lake-burst simulation, and sediment-transport analysis. Preliminary simulation models indicate the probability of multiple Late Wisconsin jökulhlaups from Lake Missoula, although these models predict a wide range of flood magnitudes. Major advances have been made in the study of low-energy, rhythmically bedded sediments that accumulated in flood slack-water areas. The ‘forty floods’ hypothesis postulates that each rhythmite represents the deposition in such slack-water areas of separate, distinct cataclysmic floods that can be traced from Lake Missoula to the vicinity of Portland, Oregon. However, the hypothesis has numerous unsubstantiated implications concerning flood magnitudes, sources, routing and sedimentation dynamics. There were multiple great Late Wisconsin floods in the Columbia River system of the northwestern United States. Studies of high-energy, high altitude flood deposits are necessary to evaluate the magnitudes of these floods. Improved geochronologic studies throughout the immense region impacted by the flooding will be required to properly evaluate flood frequency. The cataclysmic flood concept championed by J. Harlen Bretz continues to stimulate exciting and controversial research.
      7. Atwater, Brian F. “Status of glacial Lake Columbia during the last floods from glacial Lake Missoula.” Quaternary Research27.2 (1987): 182-201. The last floods from glacial Lake Missoula, Montana, probably ran into glacial Lake Columbia, in northeastern Washington. In or near Lake Columbia’s Sanpoil arm, Lake Missoula floods dating from late in the Fraser glaciation produced normally graded silt beds that become thinner upsection and which alternate with intervals of progressively fewer varves. The highest three interflood intervals each contain only one or two varves, and about 200–400 successive varves conformably overlie the highest flood bed. This sequence suggests that jökulhlaup frequency progressively increased until Lake Missoula ended, and that Lake Columbia outlasted Lake Missoula. The upper Grand Coulee, Lake Columbia’s late Fraser-age outlet, contains a section of 13 graded beds, most of them sandy and separated by varves, that may correlate with the highest Missoula-flood beds of the Sanpoil River valley. The upper Grand Coulee also contains probable correlatives of many of the approximately 200–400 succeeding varves, as do nearby parts of the Columbia River valley. This collective evidence casts doubt on a prevailing hypothesis according to which one or more late Fraser-age floods from Lake Missoula descended the Columbia River valley with little or no interference from Lake Columbia’s Okanogan-lobe dam.
      8. Benito, Gerardo. “Energy Expenditure and Geomorphic Work of the Cataclysmic Missoula Flooding in the Columbia River GGorge, USA.” Earth Surface Processes and Landforms: The Journal of the British Geomorphological Group 22.5 (1997): 457-472.  Cataclysmic releases from the glacially dammed Lake Missoula, producing exceptionally large floods, have resulted in significant erosional processes occurring over relatively short time spans. Erosional landforms produced by the cataclysmic Missoula floods appear to follow a temporal sequence in many areas of eastern Washington State. This study has focused on the sequence observed between Celilo and the John Day River, where the erosional features can be physically quantified in terms of stream power and geomorphic work. The step‐backwater calculations in conjunction with the geologic evidence of maximum flow stages, indicate a peak discharge for the largest Missoula flood of 10 × 106m3s−1. The analysis of local flow hydraulics and its spatial variation were obtained calculating the hydrodynamic variables within the different segments of a cross‐section. The nature and patterns of erosional features left by the floods are controlled by the local hydraulic variations. Therefore, the association of local hydraulic parameters with erosional and depositional flood features was critical in understanding landform development and geomorphic processes. The critical stream power required to initiate erosion varied for the different landforms of the erosional sequence, ranging from 500 W m−2 for the streamlined hills, up to 4500 W m−2 to initiate processes producing inner channels. Erosion is possible only during catastrophic floods exceeding those thresholds of stream power below which no work is expended in erosion. In fact, despite the multiple outbursts which occurred during the late Pleistocene, only a few of them had the required magnitude to overcome the threshold conditions and accomplish significant geomorphic work
      9. Clague, John J., et al. “Paleomagnetic and tephra evidence for tens of Missoula floods in southern Washington.” Geology31.3 (2003): 247-250.  Paleomagnetic secular variation and a hiatus defined by two tephra layers confirm that tens of floods from Glacial Lake Missoula, Montana, entered Washington’s Yakima and Walla Walla Valleys during the last glaciation. In these valleys, the field evidence for hiatuses between floods is commonly subtle. However, paleomagnetic remanence directions from waterlaid silt beds in three sections of rhythmically bedded flood deposits at Zillah, Touchet, and Burlingame Canyon display consistent secular variation that correlates serially both within and between sections. The secular variation may further correlate with paleomagnetic data from Fish Lake, Oregon, and Mono Lake, California, for the interval 12,000–17,000 14C yr B.P. Deposits of two successive floods are separated by two tephras derived from Mount St. Helens, Washington. The tephras differ in age by decades, indicating that a period at least this long separated two successive floods. The beds produced by these two floods are similar to all of the 40 beds in the slack-water sediment sequence, suggesting that the sequence is a product of tens of floods spanning a period of perhaps a few thousand years.
      10. Benito, Gerardo, and Jim E. O’Connor. “Number and size of last-glacial Missoula floods in the Columbia River valley between the Pasco Basin, Washington, and Portland, Oregon.” Geological Society of America Bulletin 115.5 (2003): 624-638.Field evidence and radiocarbon age dating, combined with hydraulic flow modeling, provide new information on the magnitude, frequency, and chronology of late Pleistocene Missoula floods in the Columbia River valley between the Pasco Basin, Washington, and Portland, Oregon. More than 25 floods had discharges of >1.0 × 106 m3/s. At least 15 floods had discharges of >3.0 × 106 m3/s. At least six or seven had peak discharges of >6.5 × 106 m3/s, and at least one flood had a peak discharge of ∼10 × 106 m3/s, a value consistent with earlier results from near Wallula Gap, but better defined because of the strong hydraulic controls imposed by critical flow at constrictions near Crown and Mitchell Points in the Columbia River Gorge. Stratigraphy and geomorphic position, combined with 25 radiocarbon ages and the widespread occurrence of the ca. 13 ka (radiocarbon years) Mount St. Helens set-S tephra, show that most if not all the Missoula flood deposits exposed in the study area were emplaced after 19 ka (radiocarbon years), and many were emplaced after 15 ka. More than 13 floods perhaps postdate ca. 13 ka, including at least two with discharges of >6 × 106m3/s. (6,000 years of ice sheet melt). From discharge and stratigraphic relationships upstream, we hypothesize that the largest flood in the study reach resulted from a Missoula flood that predated blockage of the Columbia River valley by the Cordilleran ice sheet. Multiple later floods, probably including the majority of floods recorded by fine- and coarse-grained deposits in the study area, resulted from multiple releases of glacial Lake Missoula that spilled into a blocked and inundated Columbia River valley upstream of the Okanogan lobe and were shunted south across the Channeled Scabland.

       

       

      AN ALTERNATIVE THEORY OF THE MISSOULA FLOODS

      BY: RANDAL CARLSON [LINK]    

      randall

      The Randall Carlson hypothesis is that the amount of energy required to melt the ice sheet and create the amount of liquid water described by researchers is 180,000 megatons. This is a staggering amount of energy. It is equivalent to 18 times the total nuclear arsenal of the USA and Russia combined. No terrestrial source of energy exists to discharge this amount of energy on an instantaneous basis. Therefore it had to be an extraterrestrial source such as asteroid or meteor perhaps a swarm asteroids that struck the ice sheet and caused it to melt all at once.

      Below is his description of the Missoula floods that closely matches the event as described in the bibliography above where ten papers are listed that agree on certain commonalities of the event. In particular the melt and floods did not occur all at once but over a period of thousands of years with somewhere between 40 to 70 melt-and-flood events separated by 50 years or more. Therefore an extraterrestrial energy source that can deliver the power of ten times the total nuclear arsenal of the USA and Russia in an instant is neither necessary nor plausible particularly so given the complete absence of evidence for such an event. The daily energy need of a 6,000-year ice melt event that needs a total of 180,000 megatons of energy is less than 7,000 joules, an amount that can be easily provided by solar irradiance reaching the surface of a 10-million-square-km ice sheet. 

      The energy balance is as follows: 180,000 megatons of TNT is 7.54E20 Joules and over a 6,000-year period it works out to 1.26E17 Joules/year or 3.98E9 watts. At 1000 watts per square meter of sunshine energy we need about 6 million square meters but we have 10 million square km at least on that ice sheet.

       

      Randall Carlson’s description of the Missoula floods is presented below. 

      1. One of the great unresolved scientific mysteries of our time concerns an extensive body of evidence for extraordinary catastrophic flooding events in the very recent geological history of North America. From the Pacific Coast of Washington State, across the mountains and prairies to the Atlantic Coast of New England, from the region of the Great Lakes to the mouth of the Mississippi, from the arid deserts of the Southwest to the lush forests of the Southern Appalachians, the geo-morphological tracks of tremendous floods of truly prodigious scale are etched indelibly into the landscape.
      2. Based upon irrefutable field evidence, these colossal floods utterly dwarf anything experienced by modern man within historical times, and yet, by geological standards they occurred exceptionally close to our own time, at the close of the most recent ice age, some 11 to 14 thousand years ago. Familiarity with the currently reigning dogmas regarding the cause of these great ice age floods would leave the casual observer with the impression that the explanation for this diluvial phenomenon has been more or less determined to the satisfaction of a majority of Earth scientists and the work remaining is only in sorting out a few particulars such as the exact number and timing of the floods.
      3. However, it is our contention that the model of causation, which is accepted at present by the overwhelming majority of geologists who have investigated the phenomenon, has inherent difficulties. We argue that researchers have not yet grasped an accurate explanation and that the currently accepted hypotheses are beset with unexamined assumptions, inconsistencies and contradictory evidence.
      4. The most impressive evidence for ancient mega-floods is found in the Pacific Northwest, primarily in Washington State, Idaho and western Montana. Here the flood features are attributed to a series of events referred to as The Missoula Floods, and these are blamed upon the repeated failure of a large ice dam that held back an enormous proglacial lake named Lake Missoula, allowing the lake to drain suddenly.
      5. The lake is supposed to have occupied the mountain valleys of Western Montana, and to have been held in by a large valley glacier in the region of Lake Pend O’rielle in northern Idaho and finally to have drained to the west across southeastern Washington. The floodwater is then assumed to have entered the great valley of the Columbia River from whence it was conveyed to the Pacific Ocean. In the process of Lake Missoula’s repeated draining a massive complex of erosional and depositional features were created that have almost no parallel on Earth.
      6. While they may have been the most spectacular, the Missoula Floods were not the only giant flood events to have occurred in North America as the great Ice Age drew to a close. The effects of mega scale flood flows have been extensively documented in the eastern foothills of the Rocky Mountains in both Canada and the U.S.; across the prairie states; in the vicinity of the Great Lakes; in Pennsylvania and western New York and in New England. All of the Canadian provinces preserve large-scale evidence of gigantic water flows. All regions within or proximal to the area of the last great glaciation show the effects of intense, mega-scale floods.
      7. Complicating the problem is the fact that areas far removed from the immediate proximity of the glaciers have not been spared the ravages of gigantic floods. The arid American southwest preserves extensive evidence of vast flooding on a scale unprecedented in modern times. The Mojave Desert of Southern California is replete with evidence of mighty flood currents drowning entire landscapes. Likewise the Sonoran Desert in Arizona and New Mexico preserves evidence of mighty flood currents. One also finds in the southeastern United States, massive erosional and depositional features in the Appalachians that allow of no other explanation than that of colossal floods. Another great flood is attributed to the catastrophic draining of Lake Bonneville, which, during the latter part of the ice age occupied large intermontane basins in Utah. The Great Salt Lake is but a diminutive remnant of this giant lake.
      8. The passage of catastrophic floods has left their mark in Pennsylvania and Western New York. The scientific documentation of these great floods reaches back into the nineteenth century, with repeated discoveries of various effects that could not be explained by invoking modern fluvial processes operating at a familiar scale, nor could they be explained by invoking glacial phenomenon. It appears that much of this continent wide flooding occurred during, or at the close of, the most recent ice age. The exact timing of the various events remains to be established. Much of the evidence points to episodic events stretching back tens of thousands of years.
      9. However, it also appears that much of this continent wide mega flooding happened concurrently at the end of the last great ice age. Evidence for megascale flooding at the end of the most recent ice age, is not limited to North America, but has been documented from all over the world. This evidence supports the conclusion that large scale super-flooding events were globally ubiquitous throughout the ice age, but occurred with exceptional power and size at or near its conclusion.
      10. Among the places around the planet from which proof is emerging of floods of extraordinary size – Siberia especially, in the Altai Mountains region near the Siberia/Mongolia border, hosts evidence for massive floods equivalent in scale and power to the largest western USA floods. Across northern Europe mega-flood evidence is found in abundance. South America, too, shows extensive evidence for massive catastrophic flooding in the recent geological past, as does Australia, New Zealand, the Middle East and Northern Africa.
      11. However, for the time being, our focus will be on the great floods of North America. Eventually, however, it will be our goal to document and correlate this imposing mass of evidence for global catastrophe with a view to understanding its origin and causes. Then, we will be in a better position to address the question of social and cultural consequences. Emerging evidence of earlier mega flood events, apparently associated with global climate changes and transition phases from glacial to interglacial ages implies a non random distribution in time, perhaps periodic or cyclical. The geographic distribution of mega-scale flood events also appears to be non-random, certain areas being affected with greater intensity than others.
      12. As stated, the Missoula Floods and Siberian floods were, as far as can be determined from field evidence at present, the greatest known freshwater floods in the history of the Earth. Other areas experienced floods of profound magnitude, but, not apparently on the scale of these two events, although the possibility of future discoveries should not be ruled out. The study of megafloods from tsunamis is a related but distinct area of palaeoflood hydrology, which in any comprehensive purview of catastrophism must be addressed. However, for now we shall limit our discussion to floods involving fresh water, meaning events related to glacial melting or rainfall.
      13. The Missoula floods were the most powerful of the great North American floods. The vast scale, the complexity and the sheer magnitude of the forces involved bestow upon these mighty events a preeminent ranking in any accounting of Earth’s great catastrophes. Even a preliminary acquaintance with the awe-inspiring after effects of this extraordinary deluge can provoke a deep sense of wonder and astonishment. Through a more prolonged acquaintance with this landscape and the story that it tells, comes a humbling realization of the almost inconceivable power of the natural forces involved.
      14. No flood events even remotely close in scale are documented from anywhere within historical times. They were one of the most significant geological occurrences in the history of the earth. Their magnitude and the release of energies involved rank them with the greatest forces of nature of which we are aware. What renders these diluvial events of exceptional importance and interest is that they occurred only yesterday in the span of geological time, and, most significantly, well within the time of Man.
      15. Let us place the great floods in context. The final phase of the last ice age, the Late Wisconsin, as it is called in reference to North America’s version of the Great Ice Age, came to a conclusion only some 12,000 to 14,000 years ago. While the effects of the ice age were global, the Late Wisconsin itself was the last episode of major ice expansion in North America at the close of the larger cycle of glacial climate called simply the Wisconsin. The final phase known as the Late Wisconsin appears to have lasted from approximately 25 or 26 thousand years before present to around 10 to 12 thousand years before present, depending upon how one defines the precise point of termination.
      16. The entire Wisconsin Ice Age lasted for around 100,000 years. While the timing and extent of glacial recessions and expansions throughout the Wisconsin Ice Age is still being worked out, it is clear that the fluctuations of climate and glacial mass during this time were considerably greater than that experience within historical times. Three ice ages in North America that were earlier than the Wisconsin have been documented by geologists and named after the states in which their glacial effects are best preserved. From oldest to youngest they were the Nebraskan, the Kansan and the Illinoian. Each of these glacial ages was separated from the next by distinct interglacial periods. The warm interval preceding the Wisconsin Ice Age and following the Illinoian is called the Sangamonian (Eemian).
      17. The European counterpart of the Wisconsin Ice Age is called the Würm, which has been extensively documented in the Alps. The signature of the Wisconsin Ice Age was, obviously, the presence of huge volumes of glacial ice where no such ice now exists. In North America this was most of Canada and a substantial amount of the northern United States. The northern boundary of the great North American ice sheet reached to the Arctic Ocean. From there south to the area now occupied by the Great Lakes the entire region was entirely buried under glacial ice. At the southern glacial margin the ice reached almost to the Ohio River in the eastern half of the U.S. New York lay under a half mile to a mile of ice. Most of the states of Wisconsin and Minnesota were buried as well as the Dakotas.
      18. The ice reached out of Canada across what is now the border, from Montana to the Pacific Ocean, with several major incursions further south in Idaho along the Rocky Mountains and in Washington State. Great glaciers also occupied many areas of the Cascades and the Sierra Nevada mountains. In all, some 6 million square miles was buried beneath a mantle of ice, about the same size as that now occupying the South Polar Region on Antarctica. Reference to this map will help to give you the big picture of the Late Wisconsin Ice Age.
      19. At the peak of the Late Wisconsin, around 18,000 to 15,000 years before present, the great ice mass reached from the Atlantic to the Pacific. However, there were actually two separate ice sheets that began separately some 5 to 7 thousand years earlier and eventually grew until they coalesced near the final stage of the Late Wisconsin. The easternmost and the larger of the two was named the Laurentide Ice sheet after a region in Quebec where it appears the ice first began accumulating. This ice sheet appears to have formed from the convergence of two centers of nucleation and outflow, one center to the east of present day Hudson Bay and one to the west.
      20. A separate ice sheet formed over the Canadian Rockies and has been designated the Cordilleran Ice Sheet by glaciologists after the collective term for the great mountain chain that forms both the Rocky Mountains and the Andes. As the Late Wisconsin reached its maximum it appears that these three ice sheets coalesced in an essentially single mass. One controversial question relates to the timing and extent of an ice free corridor between the Laurentide and Cordilleran Ice sheets, either prior to their convergence, or after, during the retreat phase.
      21. A supposition would be that humans could have utilized such an ice free corridor to migrate to the lower United States from Alaska, after crossing the Bering Land Bridge, which, of course, was exposed during the lowered sea levels of the Ice Age. As described in more detail elsewhere, through most of the late Nineteenth century and the first half of the Twentieth, it was believed that the most recent ice age was essentially an unbroken episode of global cooling and ice growth which for the most part continued uninterrupted for some 150 thousand years, or longer. It was also believed that the transitions into and out of an ice age were protracted episodes lasting tens of thousands of years.
      22. However, during the second half of the Twentieth Century, with improved dating, and with more precise and detailed stratigraphy available, it became apparent that the climate changes associated with the onset and termination of ice ages occurred much more rapidly than believed by earlier workers. As the Twentieth Century drew to a close, high-resolution records bore witness to climate changes that occurred with astonishing speed and severity. The most recent episode of widespread catastrophic flooding occurred at the termination the Late Wisconsin. Some of these floods were associated directly with melting of the glacial ice. Others are only indirectly linked to glacial melting
      23. The most powerful of the terminal ice age floods was the complex of events known as the Missoula Floods, a much more complex series of floods rather than a single large scale event. The effects of the Missoula Floods can be found imprinted upon the landscape of the Pacific Northwest from western Montana to the Pacific Ocean, and, in addition to Montana include the states of Idaho, Washington and Oregon. Our intention will be to convey an understanding of these awesome floods and to raise some questions concerning important issues that have not yet been addressed under the current state of research.
      24. The other catastrophic floods which occurred during this period of transition out of the ice age, roughly from 13,000 to 11,000 years ago, will be examined in an effort to understand the phenomenon accompanying the end of the Great Ice Age, and which, hopefully, will shed light on the most important question, which remains “What factor, or combination of factors, brought about the abrupt and extreme climate changes which terminated the ice age, and provoked catastrophic melting of the ice complex?

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

       

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