ALBERT

Description: The Last Interglacial in the Arctic region is often described as a time with warmer conditions and significantly less summer sea ice than today. The role of Atlantic water (AW) as the main oceanic heat flux agent into the Arctic Ocean remains, however, unclear. Using high-resolution stable isotope and faunal records from the only deep Arctic Gateway, the Fram Strait, we note for the upper water column a diminished influence of AW and generally colder-than-Holocene surface ocean conditions. After the main Saalian deglaciation had terminated, a first intensification of northward-advected AW happened (~124 ka). However, an intermittent sea surface cooling, triggered by meltwater release at ~122 ka, caused a regional delay in the further development towards peak interglacial conditions. Maximum AW heat advection occurred during late MIS 5e (118.5-116 ka) and interrupted a longer-term cooling trend at the sea surface that started from about 120 ka on. Such a late occurrence of the major AW-derived near-surface warming in the Fram Strait - this is in stark contrast to an early warm peak in the Holocene - compares well in time with upstream records from the Norwegian Sea, altogether implying a coherent development of south-to-north ocean heat transfer through the eastern Nordic Seas and into the high Arctic during the Last Interglacial.

Description: Paleoceanographic changes of surface water characteristics have been studied in the Nordic Seas during the Holocene and the Eemian warm periods as well as during late phases of preceding glacial periods based on a sediment core from the Iceland Sea. The age model is constrained for the Holocene by three accelerator mass spectrometry (AMS) 14C dates, correlation of some distinct and easily defined age points, obtained from the visual comparison of studied records with NPGRIP core and some tephra markers. The age model for MIS 5e is based on correlation of δ18O record to SPECMAP alongside with tephrochronolgy. Planktic foraminiferal assemblages were analyzed using the 〉150μm size fraction, foraminiferal δ13C and δ18O stable isotopes were measured on the polar planktic foraminifera N. pachyderma (s) for the Eemian period. According to high proportions of subpolar planktic forminifera (T. quinqueloba, G. bulloides, B. megastoma) during the late MIS 6, the presence of huge meltwater lids on the shelf of the Norwegian Sea was assumed resulting in deflecting of warm Atlantic water masses from its present circulation pattern towards the Iceland Sea. The proximity of the core to the Arctic and Polar fronts give possibility for their migration reconstruction. Hence, proxy records bear witness to the influence of cold fresh Polar water at the 6/5e boundary. The concomitant T. quinqueloba and B. megastoma (species that have different salinity tolerance) appearance alongside with low δ13C values evidence for subduction of warm and saline Atlantic water under fresh and cold surface water during the early part of the Last Interglacial. The same pattern is observed for the Holocene at about 10 ka cal. BP, corroborated by later T. quinqueloba appearance than G. bulloides, species that reflect Atlantic water masses. Cooling events during the periods of high solar insolation were noted and described in the current study for both interglacials. The observed reservoir ages for 8.2 – cold event is higher, by up to 200 years, than the standard model ocean. This could deflect incursions of Arctic water masses derived from the East Greenland Current to the Iceland Sea. The warmest part of the Holocene occurred in the early part (5.5-8 ka cal. BP) of the interglacial, when the insolation values were still high. In comparison the Last Interglacial 5e – ss warm period occurred with 8 ka delay only towards the end of interglacial when the isolation was low (118-122 ka cal. BP). This time lag could be explained by the huge Saalian ice sheets, inducing meltwater plumes that change the salinity gradients and resulted in easily sea ice formation. The Sea Surface Temperature (SST) reconstructions show similar values for the warmest intervals of the current and last interglacials (5oC and 2.5oC for summer and winter respectively).

Description: Climate models suggest that the Caribbean climate can be influenced by Atlantic Meridional Overturning Circulation (AMOC) variability through combined atmospheric and oceanic forcing. Specifically, when the AMOC strength is reduced, strengthening of northeasterly trades in the Caribbean is thought to drive evaporative cooling, while oceanic processes could act in opposite, warming the subsurface. To test the inferred changes across the upper water column on centennial time scales, we generated a new high-resolution proxy dataset of the last millennia from the Tobago Basin, a region in the southern Caribbean known for its open-sea upwelling. The record is comprised of stable isotopes, X-ray fluorescence, foraminiferal assemblages and alkenone-derived sea surface temperatures (SSTs). We find a robust 0.5 °C sea surface warming since the onset of the Little Ice Age (1450-1850 years AD), a climatic interval generally associated with a several degrees colder northern Caribbean. The SST increase across the Little Ice Age is interpreted to result from an intensified upwelling, which brought the oceanic-induced subsurface warmth to the sea surface, thereby contributing to a complex spatial SST pattern in the Caribbean region. The reconstructed response within the water column during the Little Ice Age is consistent with the past intervals, known for AMOC weakening, giving support for a significant role of the AMOC during the centennial-scale climatic variability of the recent past.

Description: Model simulations and proxy data from the North Atlantic reveal a high-to-low latitude teleconnection that affects the subtropical ocean circulation via ocean-atmospheric forcing. While this climatic coupling is well-studied for the last glaciation and Termination 1, it has never been investigated for the last interglacial (MIS 5e, ~129-116 ka) with sufficient resolution. Here, we close this gap by comparing records from the subarctic deep-water formation sites with new assemblage and stable isotope data from the Bahama region, an area influenced by seasonal shifts of the Intertropical Convergence Zone (ITCZ). Our proxy records from the various oceanic basins reveal for early MIS 5e a comparable millennial-scale Younger Dryas-like cooling event (~127 ka), which can be used as an important marker allowing for a better chronostratigraphic constraint of the MIS 5e interval. In the subtropical North Atlantic, the abrupt cooling could not be reconciled with insolation forcing but is associated with a sudden southward shift of the ITCZ, the latter being linked to a short-term freshwater-related reduction in strength of the ocean overturning. These results help to disentangle the roles of different mechanisms controlling low-latitude climate across MIS 5e (insolation versus oceanic and/or atmospheric versus freshwater forcing). It leads to the conclusion that a persistent high-latitude freshening and unstable deep-water overturning during early MIS 5e accounted for a “transitional” and, therefore, particularly vulnerable climatic regime during this time period, causing the cold-warm switches akin to those observed during the last glacial termination.