ALBERT

Description: Highlights • Tunisian Coral Mounds: first known to develop during the last glacial in the Mediterranean. • High surface productivity and adequate AW-LIW interface depth forced mound formation. • Distance from mounds to AW-LIW interface key in defining their formation pace. Cold-water corals are key species of benthic ecosystems, sensitive to changes in climate and capable of recording them in the chemical composition of their skeletons. The study of cold-water coral mound development in relation to palaeoceanographic variations during the Pleistocene and Holocene stages in the Mediterranean Sea has mainly been focussed in the Alboran Sea (Western Mediterranean). The present study describes the coral deposits and corresponding ages of 3 gravity cores, acquired from the newly discovered Tunisian Coral Mound Province (Central Mediterranean), which comprises several ridge-like mounds. All the cores acquired displayed dense coral deposits, dominated by Desmophyllum pertusum fragments embedded within a muddy sediment matrix. Overall, 64 coral samples have been dated with the Usingle bondTh laser ablation MC-ICP-MS method, revealing corals of mostly Pleistocene age ranging from ~MIS 11 to 8.4 ka BP. Although coral mound formation was reduced for most of the last 400 kyr, a main stage of pronounced mound formation occurred during the last glacial period, which contrasts to the findings previously published for coral mounds in other regions of the Mediterranean Sea. Coral mound formation during the last glacial was most likely associated with a colder seawater temperature than the one observed in the present-day, an increased surface productivity and an appropriate depth of the interface between Atlantic Waters and Levantine Intermediate Waters. The combination of the data acquired here with that of previous mound formation studies from the Alboran Sea also suggests that cold-water coral mounds located at greater depths develop at slower rates than those found in shallower settings.

Description: Highlights • Atlantic and Mediterranean water-mass interface depth affected coral mound growth. • Sapropel derived events had a detrimental influence on coral mound development. • A shift in the reef-building dominating coral species occurred during the Holocene. • The southern mound has been subjected to less favourable environmental conditions. Abstract Cold-water coral mounds are key hot-spots of deep ocean biodiversity and also important archives of past climatic conditions. Nonetheless, the paleo-oceanographic setting in which coral mounds developed in the Mediterranean Sea during the last 500 ka still needs to be properly understood. This study describes the coral deposits and corresponding ages of two on-mound gravity cores acquired from opposite sectors of the newly discovered Cabliers Coral Mound Province (CMP, Alboran Sea, W Mediterranean). U–Th data revealed Pleistocene-aged corals covering mound formation periods from 〉389 to 9.3 ka BP and from 13.7 to 0.3 ka BP in the southern and northern mounds respectively. The coral-rich deposits of the cores were mainly dominated by Desmophyllum pertusum, although in some sections concurrent with the Middle Pleistocene and the Holocene, other corals such as Dendrophyllia cornigera and Madrepora oculata also appeared as dominating species. Coral mound formation stages generally occurred during deglacials and temperate interstadial (3.5–4.1 δ18O‰) periods, whereas during interglacials (〈3.5 δ18O‰) coral mound formation only occurred in the northern and shallower mound. We interpret this to indicate that the shoaling of the interface between Atlantic (AW) and Levantine Intermediate Waters (LIW) during interglacial periods prevented the corals in the southern CMP from acquiring sufficient food supply, thus causing periods of coral mound stagnation. Similarly, the interruption in LIW formation throughout sapropel events also coincides with coral mound stagnation phases. This suggests that sapropel-derived processes, which originated in the eastern Mediterranean, likely affected the entire Mediterranean basin and further supports the role of LIW as a conveyor belt facilitating cold-water coral growth in the Mediterranean Sea. Overall, we show that these coral mounds yield important insights into how local changes in oceanographic conditions can influence coral mound development.

Description: Highlights • We present LGC record of the Pb isotope composition Labrador Sea seawater. • These data can be used to track Laurentide Ice Sheet extent over Hudson Bay. • LIS retreat during the PGM was relatively fast compared to the LGM • The LIS first advanced significantly over Hudson Bay during MIS 4. • Our record does not support significant LIS retreat during MIS 3. Understanding the history of continental ice-sheet growth on North America, and in particular that of the Laurentide Ice Sheet (LIS), is important for palaeoclimate and sea-level reconstructions. Information on ice-sheet extent pre-dating the Last Glacial Maximum (LGM) is heavily reliant, though, on the outputs of numerical models underpinned by scant geological data. Important aspects of LIS history that remain unresolved include the timing of its collapse during Termination 2, the first time that it expanded significantly during the Last Glacial Cycle, and whether its volume was significantly reduced during marine isotope stage (MIS) 3. To address these issues and more, we present authigenic iron-manganese (Fe–Mn) oxyhydroxide-derived high-resolution records of Pb isotope data and associated rare earth element profiles for samples spanning the past ∼130 kyr from northwest North Atlantic Labrador Sea, IODP Site U1302/3. We use these new data to track chemical weathering intensity and solute flux to the Labrador Sea associated with LIS extent on the adjacent highly radiogenic (high Pb isotope composition) North American Superior Province (SP) craton since the Penultimate Glacial Maximum (PGM). Our new records show that relatively high (radiogenic) values characterise warm marine isotope stages (MIS) 5, 3 and 1 and the lowest (most unradiogenic) values occurred during cold stages MIS 6, 4 and 2. The radiogenic Pb isotope excursion associated with Termination 2 is short-lived relative to the one documented for Termination 1, suggesting that LIS retreat during the PGM was relatively fast compared to the LGM and that its collapse during the last interglacial occurred ∼125 ka. Highly radiogenic inputs to the Labrador Sea during MIS 5d-a, ∼116–71 ka, most likely reflect a spin-up in Labrador Current vigour, incipient glaciation and renewed glacial erosion of high grounds of the eastern SP craton by localised wet-based ice-caps. A large decrease in Pb isotope values towards unradiogenic LGM-like compositions between ∼75–65 ka across the MIS 5/4 transition likely reflects a slow-down in Labrador Current vigour, an increase in subaerial deposition of aeolian dust and a significant advance of the LIS across Hudson Bay caused a strong reduction or even abandonment of Pb sourcing from the SP. The relatively radiogenic Pb isotope composition of bottom-waters bathing our study site during MIS 3, 57–29 ka, is unlikely to support a recently proposed major reduction in LIS extent for this time. Instead, we argue these values are better explained by southern Greenland Ice Sheet retreat, increased chemical weathering of the Ketelidian Mobile Belt and subsequent Pb runoff from Greenland.

Description: Highlights: • We present a T5 record of the Pb isotope composition Labrador Sea seawater. • These data can be used to track Laurentide Ice Sheet (LIS) extent over Hudson Bay. • LIS retreat during T5 occurred over longer timescales than that for T2 and T1. • LIS deglaciation played important role in protracted nature of T5 sea-level rise. • Ice retreat during T1 may not be applicable template for older terminations in GIA modelling. Termination (T) 5, ∼424 ka, involved the biggest deglaciation of land-ice mass during the Quaternary. Warming and ice-sheet retreat during T5 led to an exceptionally long period of interglacial warmth known as Marine Isotope Stage (MIS) 11, ∼424–395 ka. A detailed understanding of the history of continental ice-sheet decay during T5 is required to disentangle regional contributions of ice-sheet retreat to sea-level rise (that range between ∼1 and 13 m above present day) and to correct it for glacio-isostatic adjustments (GIA). Yet little is known about the timing and magnitude of retreat during this time of the volumetrically most important continental ice sheet in the Northern Hemisphere, the Laurentide Ice Sheet (LIS). Here we present new authigenic Fe-Mn oxyhydroxide-derived high-resolution records of Pb isotope data and associated rare earth element profiles for samples spanning T5 from Labrador Sea IODP Site U1302/3. These records feature astronomically-paced radiogenic Pb isotope excursions that track increases in chemical weathering of North American bedrock and freshwater routing to the Labrador Sea via Hudson Straits associated with LIS retreat. Our records show that LIS retreat during T5 began 429. 2 ± 7.9 ka (2σ) and likely occurred over a longer timescale (by ∼10 to 5 kyr) than that observed for T2 and T1. They also show that Hudson Bay Ice Saddle collapse (and therefore LIS break-up) occurred ∼419 ± 4.7 ka (2σ), around the same time as best estimates of southern Greenland deglaciation, but ∼12 kyr before LIS deglaciation and the sea-level high-stand associated with the latter half of MIS 11 likely occurred. Our findings therefore highlight that ice-mass loss on North America likely played an important role in the seemingly protracted nature of T5 sea-level rise. A comparison of the deglaciation histories of the LIS and the southern Greenland Ice Sheet during T5, T2 and T1 also demonstrates that the well-constrained history of regional ice-sheet retreat during T1 is not always applicable as a template for older late Pleistocene terminations in GIA modelling.