Meltwater Pulse 1A Research Articles

Timing of Cordilleran-Laurentide ice-sheet separation: Implications for sea-level rise

During the last deglaciation, collapse of the saddle between the North American Cordilleran and Laurentide ice sheets led to rapid ice-sheet mass loss and separation, with meltwater discharge contributing to deglacial sea-level rise. We directly date ice-sheet separation at the end of the saddle collapse using 64 10Be exposure ages along an ∼1200-km transect of the ice-sheet suture zone. Collapse began in the south by 15.4 ± 0.4 ka and ended by 13.8 ± 0.1 ka at ∼56°N. Ice-sheet model simulations consistent with the 10Be ages find that the saddle collapse contributed 6.2–7.2 m to global mean sea-level rise from ∼15.5 ka to ∼14.0 ka, or approximately one third of global mean sea-level rise over this period. We determine 3.1–3.6 m of the saddle collapse meltwater was released during Meltwater Pulse 1A ∼14.6-14.3 ka, constituting 20–40% of this meltwater pulse's volume. Because the separation of the Cordilleran and Laurentide ice sheets occurred over 1–2 millennia, the associated release of meltwater during the saddle collapse supplied a smaller contribution to the magnitude of Meltwater Pulse 1A than has been recently proposed.

Sea level rise drowned a vast habitable area of north-western Australia driving long-term cultural change

For most of the period of human occupation of Sahul (the combined Pleistocene landmass of Australia and New Guinea), lower sea levels exposed an extensive area of the northwest of the Australian continent, connecting the Kimberley and Arnhem Land into one vast area. Our analysis of high-resolution bathymetric data shows this now-drowned region existed as an extensive archipelago in Marine Isotope Stage 4, transforming in Marine Isotope Stage 2 into a fully exposed shelf containing an inland sea adjacent to a large freshwater lake. These were encircled by deep gorges and escarpments that likely acted as important resource zones and refugia for human populations at that time. Demographic modelling shows the shelf had a fluctuating potential carrying capacity through Marine Isotope Stages 4–2, with the capability to support 50–500 k people at various times. Two periods of rapid global sea level rise at 14.5–14.1 ka (Meltwater Pulse 1A), and between 12 ka and 9 ka, resulted in the rapid drowning of ∼50% of the Northwest Shelf. This likely caused a retreat of human populations, registering as peaks in occupational intensity at archaeological sites. We contend that the presence of an extensive archipelago on the Northwest Shelf in Marine Isotope Stage 4 facilitated the successful dispersal of the first maritime explorers from Wallacea, creating a familiar environment for their maritime economies to adapt to the vast terrestrial continent of Sahul.

Meltwater Pulse 1a drowned fringing reefs around Tahiti 15 000 years ago.

Reconstruction of postglacial sea-level rise using reef cores recovered from Tahiti during IODP Expedition 310 showed that the first major acceleration, known as Meltwater Pulse 1a (MWP-1a), was a 12-22 m rise in 340 years starting at 14.65 ka BP. Although it was reported that the pulse did not drown Tahitian reefs, the subsequent discovery of a fringing reef at the base of several cores implies that its timing, magnitude and impact require revision. Here, we report facies and paleodepth data from this reef, revise sea level, and revisit reef response. We find its reef crest is dominated by surf-adapted corals to a depth of 2.5 m and show that it retreated upslope over an approximately 1000-year interval from 16 ka. Reef development then apparently ceased at 15 ka at -106 m and remained absent for approximately 600 years, before resuming at 14.4 ka further upslope at -93 m. This absence is consistent with reef drowning and requires that MWP-1a had a smaller magnitude of 13.8 ± 1.3 m, and may have started 300 years earlier than previously reported. It confirms MWP-1a was a global event, drowning reefs on Tahiti as well as those in other oceans.

Enhanced subglacial discharge from Antarctica during meltwater pulse 1A

Subglacial discharge from the Antarctic Ice Sheet (AIS) likely played a crucial role in the loss of the ice sheet and the subsequent rise in sea level during the last deglaciation. However, no direct proxy is currently available to document subglacial discharge from the AIS, which leaves significant gaps in our understanding of the complex interactions between subglacial discharge and ice-sheet stability. Here we present deep-sea coral 234U/238U records from the Drake Passage in the Southern Ocean to track subglacial discharge from the AIS. Our findings reveal distinctively higher seawater 234U/238U values from 15,400 to 14,000 years ago, corresponding to the period of the highest iceberg-rafted debris flux and the occurrence of the meltwater pulse 1A event. This correlation suggests a causal link between enhanced subglacial discharge, synchronous retreat of the AIS, and the rapid rise in sea levels. The enhanced subglacial discharge and subsequent AIS retreat appear to have been preconditioned by a stronger and warmer Circumpolar Deep Water, thus underscoring the critical role of oceanic heat in driving major ice-sheet retreat.

Late Pleistocene and Holocene transgression inferred from the sediments of the Gulf of San Jorge, central Patagonia, Argentina

ABSTRACTThis study presents the first detailed description of the upper sedimentary succession of the late Pleistocene and Holocene deposits in the Gulf of San Jorge (Patagonia) based on several hundred kilometers of high‐resolution seismic (sparker) profiles and numerous sediment cores. High‐resolution seismic stratigraphy confirms the existence of a paleo‐fluvial network formed during sea‐level lowstands and buried by central basin estuarine deposits during the last marine transgression. Analyses of lithostratigraphy and radiocarbon ages indicate the onset of subtidal sedimentation at ~14 cal ka bp. Before the onset of subtidal conditions, the first steps of marine incursion seem to have led to the development of lagoonal/wind–tidal flat environments, advocating for a sea‐level stillstand. An abrupt increase in the log(Ti/Ca) ratio in a distinct multi‐centimeter‐thick layer and the identification of a wave‐ravinement surface suggest rapid sea‐level rise in the gulf prior to ~14 cal ka bp, consistent with Meltwater Pulse 1A. Overall, this study highlights the significant impact of sea‐level rise on sedimentation in the gulf from the onset of marine incursions to the mid‐Holocene, as well as the reduced contribution, as currently observed, of riverine inputs due to the progressive diminution and withdrawal of glacial drainage starting before the Holocene.

Transient rheology in sea level change: Implications for Meltwater Pulse 1A

Ice mass and sea-level changes occur at many timescales inducing glacial isostatic adjustment (GIA). Typically, the solid Earth is treated as a Maxwell viscoelastic solid when predicting GIA at timescales from the peak of the ice age to present day (∼21,000 yr before present). For events occurring at shorter (daily-centennial) timescales, the solid Earth is often treated as an elastic solid. Experimental results within the rock mechanics community indicate that transient deformation occurs at intermediate timescales, neither captured by a Maxwell or elastic mechanical model. With realistic, experimentally constrained viscoelastic models, we explore transient deformation in short-, intermediate-, and long-term GIA measurements, then turn to Meltwater Pulse 1A (MWP-1A). MWP-1A occurred ∼14,500 yr ago and represents an event during which global mean sea level rose by ∼ 20 m within a timespan of, at most, 500 yr. With newly computed transient deformation, sea-level change predictions deviate substationally (∼1–2 m) from the Maxwell model at classic locations (Barbados, Sunda Shelf, Tahiti) that record MWP-1A sea level. These records are used to constrain the melt source of MWP-1A with important implications on ice sheet stability and the climate of a warming Earth. Our results suggest a timely need to revisit the source of MWP-1A and other analogous events.

Meltwater Pulse1A Triggered an Extreme Cooling Event: Evidence From Southern China

AbstractMeltwater Pulse 1A injection into the North Atlantic coincided with the Bølling warming event, despite climate model simulations indicating that the Meltwater Pulse 1A should have inevitably lead to an extreme cooling in the northern hemisphere. However, so far no cooling event has been found in paleoclimate records responding to Meltwater Pulse 1A. Here we reconstruct winter temperature based on sedimentary diatoms from Huguangyan Maar Lake in tropical China. The results show that winter temperature dropped by at least 6°C within ∼100 years at 14.8 ± 0.02 ka BP, coeval with the onset of Meltwater Pulse 1A, within dating uncertainty. We argue that Meltwater Pulse 1A weakened the Atlantic Meridional Overturning Circulation (AMOC), resulting in abrupt severe cooling in the Northern Hemisphere that caused a severe winter temperature drop in East Asia by strengthening the winter monsoon. We propose that extreme cooling in winter temperature triggered the Bølling warming by stopping the freshwater release from the ice‐sheet, triggering the AMOC to recover quickly and causing the Bølling event as an overshoot under gradual forcing.

Deglacial release of petrogenic and permafrost carbon from the Canadian Arctic impacting the carbon cycle

The changes in atmospheric pCO2 provide evidence for the release of large amounts of ancient carbon during the last deglaciation. However, the sources and mechanisms that contributed to this process remain unresolved. Here, we present evidence for substantial ancient terrestrial carbon remobilization in the Canadian Arctic following the Laurentide Ice Sheet retreat. Glacial-retreat-induced physical erosion of bedrock has mobilized petrogenic carbon, as revealed by sedimentary records of radiocarbon dates and thermal maturity of organic carbon from the Canadian Beaufort Sea. Additionally, coastal erosion during the meltwater pulses 1a and 1b has remobilized pre-aged carbon from permafrost. Assuming extensive petrogenic organic carbon oxidation during the glacial retreat, a model-based assessment suggests that the combined processes have contributed 12 ppm to the deglacial CO2 rise. Our findings suggest potentially positive climate feedback of ice-sheet retreat by accelerating terrestrial organic carbon remobilization and subsequent oxidation during the glacial-interglacial transition.

Ancient marine sediment DNA reveals diatom transition in Antarctica

Antarctica is one of the most vulnerable regions to climate change on Earth and studying the past and present responses of this polar marine ecosystem to environmental change is a matter of urgency. Sedimentary ancient DNA (sedaDNA) analysis can provide such insights into past ecosystem-wide changes. Here we present authenticated (through extensive contamination control and sedaDNA damage analysis) metagenomic marine eukaryote sedaDNA from the Scotia Sea region acquired during IODP Expedition 382. We also provide a marine eukaryote sedaDNA record of ~1 Mio. years and diatom and chlorophyte sedaDNA dating back to ~540 ka (using taxonomic marker genes SSU, LSU, psbO). We find evidence of warm phases being associated with high relative diatom abundance, and a marked transition from diatoms comprising <10% of all eukaryotes prior to ~14.5 ka, to ~50% after this time, i.e., following Meltwater Pulse 1A, alongside a composition change from sea-ice to open-ocean species. Our study demonstrates that sedaDNA tools can be expanded to hundreds of thousands of years, opening the pathway to the study of ecosystem-wide marine shifts and paleo-productivity phases throughout multiple glacial-interglacial cycles.

10Be exposure age dating of Late Quaternary relative sea level changes and deglaciation of W Jura and NE Islay, Scottish Inner Hebrides

ABSTRACTNew 10Be exposure age dating and geomorphological mapping of emerged shoreline features in W Jura and NE Islay throw new light on the regional pattern of ice sheet deglaciation and late-glacial relative sea level change. We conclude that the oldest and highest emerged shorelines in this area were produced ~15.7–16.3 ka, shortly after ice sheet deglaciation ~16.5 ka. It is envisaged that the first incursion of marine waters into coastal areas took place close to a former ice sheet margin that oscillated in position across this part of the Scottish Inner Hebrides. The first evidence of late-glacial marine sedimentation following deglaciation consists of emerged marine terrace fragments and unvegetated gravel beach ridges, the former represented by a prominent glacio-isostatically tilted shoreline that declines in altitude NE to SW, from ~40 m above ordnance datum (OD) in NW Jura to ~19 m OD in central Islay. In W Jura, north of Loch Tarbert, spectacular staircases of up to 55 unvegetated gravel beach ridges were formed shortly after regional deglaciation, possibly within 1 ka. A preliminary estimate of the average rate of relative sea level lowering across W Jura between deglaciation and the Younger Dryas is in the order of ~7 mmyr−1. Geomorphological evidence from Shian Bay, W Jura, indicates a truncation of the late-glacial beach ridge staircases by a large 480-m-long beach ridge (the Colonsay Ridge) at ~14.9 ka, when former relative sea level was at ~18 m OD. This ridge may represent the product of either a stillstand in the progressive lowering of relative sea level during the late-glacial or a reversal. This raises the intriguing possibility of an association between ridge formation and the timing of the well-established global meltwater pulse 1A between ~14.65 and ~14.8 ka.

When did Goliath collapse? Dating the recent events of a major submarine slide complex, Southeastern Mediterranean margin

Unraveling the failure history of submarine slides and delineating its environmental controls are crucial for practical hazard assessments, but are commonly challenging and costly. Here we address this challenge by investigating the Goliath slide complex, one of the largest documented slide scars on the ~200 km long continental slope offshore Israel. Geophysical evidence suggest that the Goliath complex is a relatively young feature. However, despite its proximity to submarine infrastructure and to one of the most populated coastal areas in the Mediterranean, its recent temporal development was never determined.Based on a detailed analysis of sub-meter resolution multi-channel seismic profiles, four sediment cores were retrieved from the northern head scarp and toe domains of the Goliath slide complex. Selective sedimentological and chronological analyses were carried out following a detailed computed tomography analysis of the cores. The results reveal two generations of deposits on the northern head scarp of Goliath, separated by a detachment surface. Two 14C ages of 7.46 ± 0.13 cal ka BP (core PHS-1) and 7.38 ± 0.16 cal ka BP (core PHS-5) were obtained for the sediments immediately overlying this surface, implying that the Goliath northern head scarp was formed, at least in part, during a substantial ~7.4 cal ka BP event. A ~3.7 kyrs hiatus within the late Holocene sedimentary sequence of core PHS-5 may suggest an additional, more recent and presumably smaller, slide event that occurred at ~2.4 ka BP. The sedimentary succession from Goliath's toe domain (core PTL-3), located ~32 km downslope from the head scarp, show an upper 1.2 m long continuous undisturbed sequence dated to the last ~14 ka BP and including sapropel S1 deposits. This sequence overlies three disturbed units, interpreted as mass transport deposits (MTDs) containing various deformation features, large-scale burrows, sharp contacts and fold structures. A 14C age dates the base of the hemipelagic sequence to 13.91 ± 0.23 cal ka BP, representing the minimum age of the slide event that deposited this MTD. Ages within the MTD units are substantially older (18.21 ± 0.27 to 28.66 ± 0.33 cal ka BP) than in the overlying sequence and an age-inversion within the MTDs supports their interpretation as transported sediments.The timing of the prominent slide events in the Goliath complex corresponds with the late stages of meltwater pulses 1A (~14.6–13.7 ka BP) and 1C (~8.2–7.5 ka BP), periods of accelerated sea level rise and probably increased sediments supply. Our results suggest that climate-driven factors likely contributed significantly to slope instability in this area, while earthquakes on the Dead Sea Transform may have been the triggering factor for the Goliath Slide events.

Local oceanic CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; outgassing triggered by terrestrial carbon fluxes during deglacial flooding

Abstract. Exchange of carbon between the ocean and the atmosphere is a key process that influences past climates via glacial–interglacial variations of the CO2 concentration. The melting of ice sheets during deglaciations induces a sea level rise which leads to the flooding of coastal land areas, resulting in the transfer of terrestrial organic matter to the ocean. However, the consequences of such fluxes on the ocean biogeochemical cycle and on the uptake and release of CO2 are poorly constrained. Moreover, this potentially important exchange of carbon at the land–sea interface is not represented in most Earth system models. We present here the implementation of terrestrial organic matter fluxes into the ocean at the transiently changing land–sea interface in the Max Planck Institute for Meteorology Earth System Model (MPI-ESM) and investigate their effect on the biogeochemistry during the last deglaciation. Our results show that during the deglaciation, most of the terrestrial organic matter inputs to the ocean occurs during Meltwater Pulse 1a (between 15–14 ka) which leads to the transfer of 21.2 Gt C of terrestrial carbon (mostly originating from wood and humus) to the ocean. Although this additional organic matter input is relatively small in comparison to the global ocean inventory (0.06 %) and thus does not have an impact on the global CO2 flux, the terrestrial organic matter fluxes initiate oceanic outgassing in regional hotspots like in Indonesia for a few hundred years. Finally, sensitivity experiments highlight that terrestrial organic matter fluxes are the drivers of oceanic outgassing in flooded coastal regions during Meltwater Pulse 1a. Furthermore, the magnitude of outgassing is rather insensitive to higher carbon-to-nutrient ratios of the terrestrial organic matter. Our results provide a first estimate of the importance of terrestrial organic matter fluxes in a transient deglaciation simulation. Moreover, our model development is an important step towards a fully coupled carbon cycle in an Earth system model applicable to simulations at glacial–interglacial cycles.

Slow and soft passage through tipping point of the Atlantic Meridional Overturning Circulation in a changing climate

Paleo-proxy records suggest that the Atlantic Meridional Overturning Circulation (AMOC) exhibits a threshold for an abrupt change, a so-called tipping point. A classical bifurcation theory, a basis of the tipping dynamics of AMOC implicitly assumes that the tipping point is fixed. However, when a system is subjected to time-varying forcing (e.g., AMOC exposed to ice meltwater) an actual tipping point can be overshot due to delayed tipping, referred to as the slow passage effect. Here, using an Earth system model of intermediate complexity and a low-order model with freshwater forcing, we show that the tipping point of AMOC is largely delayed by the slow passage effect. It causes a large tipping lag of up to 1300 years, and strongly relaxes the abruptness of tipping as well. We further demonstrate that the tipping modulation can actively occur in past, present, and future climates by quantifying the effect during Dansgaard-Oeschger events, meltwater pulse 1A (MWP-1A), and current Greenland ice sheet melting. The suggested slow passage effect may explain the observed lagged AMOC collapse to MWP-1A of about 1000 years and provides implications tipping risk in the future.

Glacial isostatic adjustment near the center of the former Patagonian Ice Sheet (48°S) during the last 16.5 kyr

Our understanding of glacial isostatic rebound across Patagonia is highly limited, despite its importance to constrain past ice volume estimates and better comprehend relative sea-level variations. With this in mind, our research objective is to reconstruct the magnitude and rate of Late Glacial and Holocene glacial isostatic adjustment near the center of the former Patagonian Ice Sheet. We focus on Larenas Bay (48°S; 1.26 km2), which is connected to Baker Channel through a shallow (7.4 m) and narrow (ca. 150 m across) inlet, and hence has the potential to record periods of basin isolation and marine ingression. The paleoenvironmental evolution of the bay was investigated through a sedimentological analysis of a 9.2 m long radiocarbon-dated sediment core covering the last 16.8 kyr. Salinity indicators, including diatom paleoecology, alkenone concentrations and CaCO3 content, were used to reconstruct the bay's connectivity to the fjord. Results indicate that Larenas Bay was a marine environment before 16.5 cal kyr BP and after 9.1 cal kyr BP, but that it was disconnected from Baker Channel in-between. We infer that the postglacial rebound started before 16.5 cal kyr BP and that it outpaced global sea-level rise until slightly before 9.1 cal kyr BP. During the Late Glacial and early Holocene, the center of the former Patagonian Ice Sheet experienced an absolute uplift of ca. 96 m, at an average rate of 1.3 cm/yr. During the remainder of the Holocene, glacial isostatic adjustment continued (ca. 20 m), but at a slower average pace of 0.2 cm/yr. Comparisons between multi-millennial variations in the salinity indicators and existing records of global sea-level rise suggest that the glacial isostatic adjustment rate also fluctuated within these time intervals, likely in response to glacier dynamics. More specifically, most of the glacial isostatic adjustment registered between 16.5 – 9.1 cal kyr BP seems to have occurred before meltwater pulse 1A (14.5 – 14.0 kyr BP). Likewise, it appears that the highest glacial isostatic rebound rates of the last 9.1 kyr occurred during the late Holocene, most likely in response to glacier recession from their Neoglacial maxima. This implies a relatively rapid response of the local solid earth to ice unloading, which agrees with independent modelling studies investigating contemporary uplift. We conclude that the center of the former Patagonian Ice Sheet experienced a glacial isostatic adjustment of ca. 116 m over the last 16.5 kyr, and that >80% occurred during the Late Glacial and early Holocene.

Hydroclimate response in Texas and Gulf of Mexico to rapid warming during the last deglacial: High-resolution speleothem proxy and monitoring evidence

Cave calcite (i.e., speleothem) proxy records that span abrupt warming events, such as those of the last deglacial, may prologue regional responses of hydroclimate to 21st century warming. Proxy reliability is advanced by an understanding of the modern hydrologic system and controls on calcite growth. Here we integrate monitoring of Cave CWN in central Texas with high-resolution imaging and δ18O analysis of Stalagmite CWN-4 to understand how regional hydroclimate changed during a rapid deglacial warming event - the transition from Heinrich Stadial 1 (HS1) to the Bølling-Allerød (BA) warm period. This event is recorded in CWN-4 as a rapid negative δ18O excursion of 1.7‰ over ∼210 years (HS1-BA δ18O excursion = ‘HBO’), followed by a 6-fold growth rate increase.Monitoring demonstrates that modern calcite grows during cool seasons, growth rates follow drip rate, and drip water and calcite δ18O reflect the δ18O of recharge. Because drip waters have interannual epikarst residence times, their δ18O values are well-mixed averages of their Gulf of Mexico (GoM) moisture source δ18O values, which rapidly decreased during Laurentide Ice Sheet (LIS) melting events. Confocal laser fluorescence microscopy imaging indicates that growth lamina are seasonal within U-series age constraints. The timing of the HBO (14.75 ± 0.08 to 14.54 ± 0.08 ka), corresponds with 1) the onset of Bølling warming in Greenland (14.64 ka), 2) AMOC reinvigoration (∼14.61–14.25 ka), 3) Meltwater Pulse 1a (14.65–14.31 ka), and 4) Meltwater Flood 3 (MWF-3) - the most intense episode of LIS meltwater discharge into the GoM (14.97–14.46 ka). The rapid increase in growth rates following the HBO indicates an abrupt transition to a wetter hydroclimate in central Texas following these regional and global events.The HBO δ18O excursion occurred monotonically, consistent with meltwater discharge being continuous. This excursion also corresponds with climate change recognized across the HS1-BA transition in marine and terrestrial records influenced by changes in North Atlantic climate, AMOC, and ITCZ migrations. We infer that central Texas deglacial hydroclimate largely followed changes in AMOC, linked via meltwater input to the GoM. Periods of fast (slow) speleothem growth coincide with warmer (cooler) North Atlantic episodes, with the exception of the HS1 to BA transition. For this transition, slow growth rates during MWF-3 may reflect protracted cooling of GoM SST and corresponding atmospheric moisture reduction. The common timing and duration of the HBO with shifts toward wetter conditions across the HS1-BA transition in many northern Hemisphere climate records supports common ocean-atmosphere teleconnections related to AMOC intensity.

Freshwater routing in eddy-permitting simulations of the last deglacial: the impact of realistic freshwater discharge

Abstract. Freshwater, in the form of glacial runoff, is hypothesized to play a critical role in centennial- to millennial-scale climate variability, such as the Younger Dryas and Dansgaard–Oeschger events, but this relationship is not straightforward. Large-scale glacial runoff events, such as Meltwater Pulse 1a (MWP1a), are not always temporally proximal to subsequent large-scale cooling. Moreover, the typical design of hosing experiments that support this relationship tends to artificially amplify the climate response. This study explores the impact that limitations in the representation of runoff in conventional “hosing” simulations has on our understanding of this relationship by examining where coastally released freshwater is transported when it reaches the ocean. We particularly focus on the impact of (1) the injection of freshwater directly over sites of deep-water formation (DWF) rather than at runoff locations (i.e. hosing), (2) excessive freshwater injection volumes (often by a factor of 5), and (3) the use of present-day (rather than palaeo) ocean gateways. We track the routing of glaciologically constrained freshwater volumes from four different inferred injection locations in a suite of eddy-permitting glacial ocean simulations using the Massachusetts Institute of Technology General Circulation Model (MITgcm) under both open and closed Bering Strait conditions. Restricting freshwater forcing values to realistic ranges results in less spreading of freshwater across the North Atlantic and indicates that the freshwater anomalies over DWF sites depend strongly on the geographical location of meltwater input. In particular, freshwater released into the Gulf of Mexico generates a very weak freshwater signal over DWF regions as a result of entrainment by the turbulent Gulf Stream. In contrast, freshwater released into the Arctic with an open Bering Strait or from the Eurasian ice sheet is found to generate the largest salinity anomalies over DWF regions in the North Atlantic and GIN (Greenland–Iceland–Norwegian) seas region respectively. Experiments show that when the Bering Strait is open, the Mackenzie River source exhibits more than twice as much freshening of the North Atlantic deep-water formation regions as when the Bering Strait is closed. Our results illustrate that applying freshwater hosing directly into the North Atlantic with even “realistic” freshwater amounts still overestimates the amount of terrestrial runoff reaching DWF regions. Given the simulated salinity anomaly distributions and the lack of reconstructed impact on deep-water formation during the Bølling–Allerød, our results support that the majority of the North American contribution to MWP1a was not routed through the Mackenzie River.

Sedimentation and organic content in the mires and other sites of sediment accumulation in the Sydney region, eastern Australia, in the period after the Last Glacial Maximum

This research reports on a synthesis of radiocarbon (14C) dates and the organic content from a variety of depositional sites in a relatively small region in humid eastern Australia centred on Sydney. We focused on basal dates, changes in accumulation rates and the organic content of these sediment records in the period post-dating 21 thousand years ago to make inferences about past environmental conditions, or to infer the timing of past environmental change. We found that low rates of sediment and organic accumulation at the Last Glacial Maximum continued well into the late Pleistocene. The average rate of sediment deposition and organic content increased from about 14.5 calibrated kiloanni before present (cal ka BP), perhaps coincident with Meltwater Pulse 1A, but this was then checked by dry conditions during the Antarctic Climatic Reversal chronozone. An abrupt increase in the average rate of sediment accumulation coincided with the Pleistocene-Holocene boundary (at 11.7 cal ka BP), and this continued until about 9.2 cal ka BP, largely coinciding with the Antarctic thermal maximum, and probably reflecting reduced moisture availability in the Sydney region. Indication of depressed temperature and a more positive moisture availability, from about 9 to 7.6 cal ka BP, witnessed the fastest increase in the number of sites than at any other time. An overall drier early Holocene abruptly altered at about 7.5 cal ka BP and a mid-Holocene ‘optimum’ in moisture availability extended to 6.2 cal ka BP. The compilation of organic contents of the mid-late Holocene suggests environmental variability, but El Niño frequency or strength is not implicated as a driving force. Increased organic productivity, especially after 2.8 cal ka BP, corresponded to a peak in summer insolation, and associated seasonality of insolation and this is likely to have resulted in increased, or more consistent, summer rainfall and easterly air flow into the Sydney region. In contrast to previous generalisations about changes in south-eastern Australia during the Holocene, which have often relied on palaeoenvironmental records from further south, the southward migration of the intertropical convergence zone during the Holocene had vastly different synoptic outcomes in the Sydney region, with the early Holocene drier as continental air dominated, and the late Holocene wetter, as the synoptic conditions saw more tropical and easterly airflow. This work demonstrates the danger in making generalisations across regions and highlights the utility of the compilation of data at a homoclimatic, regional scale.

Local and regional constraints on relative sea‐level changes in southern Isle of Skye, Scotland, since the Last Glacial Maximum

ABSTRACTNew relative sea‐level (RSL) data constrain the timing and magnitude of RSL changes in the southern Isle of Skye following the Last Glacial Maximum (LGM). We identify a marine limit at ~23 m OD, indicating RSL ~20 m above present c. 15.1 ka. Isolation basin data, supported by terrestrial and marine limiting dates, record an RSL fall to 11.59 m above present by c. 14.2 ka. This RSL fall occurs across the time of global Meltwater Pulse 1A, supporting recent research on the sources of ice melting. Our new data also help to resolve some of the chronological issues within the existing Isle of Skye RSL record and provide details of the sub‐Arctic marine environment associated with the transition into Devensian Lateglacial climate at c. 14.5 k cal a bp, and the timing of changes in response to the Loch Lomond Stadial climate. Glacio‐isostatic adjustment (GIA) model predictions of RSL deviate from the RSL constraints and reflect uncertainties in local and global ice models used within the GIA models. An empirical RSL curve provides a target for future research.

Ice thinning on nunataks during the glacial to interglacial transition in the Antarctic Peninsula region according to Cosmic-Ray Exposure dating: Evidence and uncertainties

The small ice caps distributed across the Antarctic Peninsula region have undergone large ice volume changes since the Last Glacial Cycle, in line with most of the Antarctic continent. While the surface extent of glacial shrinking is relatively well known, the timing of glacial oscillations and the magnitude of ice thinning remain little investigated. Cosmic-Ray Exposure (CRE) dating applied on ice-free vertical sequences can provide insights about the temporal framework of glacial oscillations. However, the potential occurrence of nuclide inheritance may overestimate the real timing of the last glacial retreat. This problem has been observed in many areas in Continental Antarctica, but similar studies have not yet been conducted in environments of the Maritime Antarctica, such as the South Shetland Islands (SSI). This research focuses on the Hurd Peninsula ice cap (HPIC, ca. 60°22′ W, 62°40’ S), located in the SW of Livingston Island, SSI. Past climate oscillations since the Last Glacial Cycle have determined the amount of ice stored in the ice cap. Today, this polythermal ice cap is surrounded by several nunataks standing out above the ice. Three of them have been selected to explore their deglaciation history and to test the potential occurrence of nuclide inheritance in deglaciated bedrocks associated with polythermal glaciers. We present a new dataset with 10 10Be exposure dates. Some of them were found to be anomalously old, evidencing that nuclide inheritance is present in bedrocks associated with polythermal ice caps and suggesting complex glacial exposure histories. We attribute this to limited erosion, given the gentle slope of the nunatak margins and the cold-based character of the surrounding ice. The remaining samples allowed to approach local surface-elevation changes of the HPIC. Our results suggest that ice thinning started during the Last Glacial Maximum (LGM) at ∼22 ka but intense glacial shrinking occurred from ∼18 to ∼13 ka, when the nunataks became exposed, being particularly intense at the end of this period (∼14–13 ka) coinciding with the time of the meltwater pulse 1a (MWP-1a) and the end of the Antarctic Cold Reversal (ACR).

An Ancient Meltwater Pulse Raised Sea Levels by 18 Meters

Meltwater pulse 1A, a period of rapid sea level rise after the last deglaciation, was powered by melting ice from North America and Scandinavia, according to new research.