ALBERT

Description: A marine sediment core from Vaigat in Disko Bugt, West Greenland, has been analysed in terms of lithology, dinoflagellate cysts and foraminifera in order to evaluate the influence of oceanographic variability on West Greenland glacier stability. The data show that during the past 5200 years the Atlantic foraminiferal abundance in the subsurface waters of the West Greenland Current (WGC) episodically increased, indicating periods of increases in the inflow of subsurface warm Atlantic water at 2000 - 1500 cal. yr BP and 1300 cal. yr BP as well as periods of less pronounced increased bottom-water temperatures around 4700 - 4000 cal. yr BP, 3100 - 2800, 2600, 1000 - 800, 500 - 400, and at 200 cal. yr. The sedimentological and dinoflagellate cyst data indicate that these episodes with enhanced advection of Irminger Sea-derived waters are accompanied by increased iceberg rafting, which we link to increased iceberg calving in relation to destabilization of the Jakobshavn Isbrae. The long-term trend in the data documents the end of a late-Holocene Thermal Maximum between 5200 and 4300 cal. yr BP and a final onset of the Neoglaciation at 3500 cal. yr BP. Increased responses of the iceberg rafting after 3500 cal. yr BP, reflects a westward/seaward advance of the glacier margin in relation to onset of Neoglaciation and a development of the glacier into a floating tongue after 2000 cal. yr BP. A comparison of our record with a record from the eastern North Atlantic indicates that a NAO-like anomaly pattern between subsurface waters in West Greenland and atmospheric temperature in the Eastern North Atlantic may have been operating during most of the late Holocene. However, during the past 1000 years the NAO signal may have weakened as some other mode of climate variability overprints the anti-phase climate signal in this region.

Description: As an update to the RTopo-2.0.1 data set (https://doi.org/10.1594/PANGAEA.856844), RTopo-2.0.4 contains new original bathymetry data for the Northeast Greenland continental shelf. In the Southern Ocean, we added the Rosier et al. (JGR Oceans, 2018) bathymetry grid below Filchner Ice Shelf. This work was supported in part through the Deutsche Forschungsgemeinschaft (DFG) within the Special Priority Program (SPP) 1889 "Regional Sea Level Change and Society" (grant OGreen79), the German Federal Ministry for Education and Research (BMBF) within the GROCE project (Grant 03F0778A), the Natural Environment Research Council (NERC) large grant "Ice shelves in a warming world: Filchner Ice Shelf System" (NE/L013770/1), the NERC project "Greenland in a warmer climate: What controls the advance & retreat of the NE Greenland Ice Stream" (Grant NE/N011228/1), and the Helmholtz Climate Initiative "Regional Climate Change" (REKLIM).

Description: As an update to the Northeast Greenland - Digital Bathymetric Compilation (https://doi.pangaea.de/10.1594/PANGAEA.849313), the updated digital bathymetric model (DBM) for the Northeast Greenland (NEG) continental shelf (74°N - 81°N) contains new original bathymetry data for the Northeast Greenland continental shelf, specifically in front of the 79 North Glacier, recorded during R/V Polarstern expedition PS100. This work was supported in part through the Deutsche Forschungsgemeinschaft (DFG) within the Special Priority Program (SPP) 1889 "Regional Sea Level Change and Society" (grant OGreen79), the German Federal Ministry for Education and Research (BMBF) within the GROCE project (Grant 03F0778A), and the NERC project "Greenland in a warmer climate: What controls the advance & retreat of the NE Greenland Ice Stream" (Grant NE/N011228/1).

Description: Precise relative sea level (RSL) data are important for inferring regional ice sheet histories, as well as helping to validate numerical models of ice sheet evolution and glacial isostatic adjustment. Here we develop a new RSL curve for Fildes Peninsula, South Shetland Islands (SSIs), a sub-Antarctic archipelago peripheral to the northern Antarctic Peninsula ice sheet, by integrating sedimentary evidence from isolation basins with geomorphological evidence from raised beaches. This combined approach yields not only a Holocene RSL curve, but also the spatial pattern of how RSL change varied across the archipelago. The curve shows a mid-Holocene RSL highstand on Fildes Peninsula at 15.5 m above mean sea level between 8000 and 7000 cal a BP. Subsequently RSL gradually fell as a consequence of isostatic uplift in response to regional deglaciation. We propose that isostatic uplift occurred at a non-steady rate, with a temporary pause in ice retreat ca. 7200 cal a BP, leading to a short-lived RSL rise of ~1 m and forming a second peak to the mid-Holocene highstand. Two independent approaches were taken to constrain the long-term tectonic uplift rate of the SSIs at 0.22-0.48 m/ka, placing the tectonic contribution to the reconstructed RSL highstand between 1.4 and 2.9 m. Finally, we make comparisons to predictions from three global sea level models.

Description: Successful application of the alkenone palaeothermometer, the UK'37 index, relies upon the assumption that fossil alkenone synthesisers responded to growth-temperature changes in a similar manner to the modern producers, chiefly the coccolithophores Emiliania huxleyi and Gephyrocapsa oceanica. We compare coccolith and UK'37 data from ODP Site 1087 in the south-east Atlantic between 1500 and 500 ka, and show that evolutionary events and changes in species dominance within the coccolithophore populations had little impact on the UK'37 record. The relative abundances of the C37 and C38 alkenones also closely resembled those found in modern populations, and suggest a similar temperature sensitivity of UK'37 during the early and mid-Pleistocene to that found at present. These results support the application of the UK'37 index to reconstruct sea-surface temperatures (SSTs) throughout the Quaternary. The UK'37 record at ODP Site 1087 contains an SST signal that documents the emergence of the 100-kyr cycles that characterise the late Quaternary ice volume records. This is preceded by significant cooling at ODP Site 1087, marked by a negative shift in SSTs and a positive shift in the planktonic delta18O some 250-kyr earlier, at ca 1150-1000 ka. This results in a permanent fall in average SSTs of around 1.5 °C. The predicted increase in aridity onshore as a result of this cooling can be identified in a number of published records from southern Africa, and may have played a role in some important evolutionary events of the mid-Pleistocene.

Description: Alkenone data from ODP Site 983 (UK37, UK'37 and %C37:4) spanning the 0.5-1.5 Ma interval, used to reconstruct sea surface temperatures and polar water mass expansion during the mid-Pleistocene transition (MPT). Past surface ocean circulation changes associated with the mid‐Pleistocene transition, 0.9-0.6 Ma, were reconstructed in the northern North Atlantic (ODP 983) using proxies for subarctic/subpolar water mass distributions (%C37:4 alkenone) and sea surface temperature (UK37, UK'37). A secular expansion of subarctic waters occurred from ∼1.15 Ma, spanning both glacial and interglacial intervals. After 0.9 Ma, low %C37:4 at Site 983 records a northward retreat of subarctic waters during interglacials in the Atlantic, while continued high glacial %C37:4 indicate extensive subarctic waters during glacial maxima associated with the development of the larger late Pleistocene ice sheets. It is proposed that the expansion of subarctic waters between 1.15 and 0.9 Ma exerted negative feedbacks to the moisture supply to the ice sheet source regions and may account for the apparent delayed ice sheet response to atmosphere‐ocean circulation changes associated with the mid‐Pleistocene transition that began as early as 1.2 Ma.