A warm and poorly ventilated deep Arctic Mediterranean during the last glacial period

Abstract

Changes in the formation of dense water in the Arctic Ocean and Nordic Seas (the 'Arctic Mediterranean', AM) likely contributed to the altered climate of the last glacial period. We examine past changes in AM circulation by reconstructing 14 C ventilation ages of the deep Nordic Seas over the last 30,000 years. Our results show that the deep glacial AM was extremely poorly ventilated (ventilation ages of up to 10,000 years). Subsequent episodic overflow of aged water into the mid-depth North Atlantic occurred during deglaciation. Proxy data also suggest the deep glacial AM was ~2-3°C warmer than modern; deglacial mixing of the deep AM with the upper ocean thus potentially contributed to melting sea-ice and icebergs, as well as proximal terminal icesheet margins.One Sentence Summary: New proxy data reveals the extremely poor ventilation of a warmer, glacial deep Arctic Mediterranean, which overflowed into the Northeast Atlantic during the last deglaciation. Main Text:The Atlantic meridional overturning circulation (AMOC) plays an important role in Earth's climate because it redistributes ocean heat and helps control the storage of carbon in the deep ocean. The primary northern hemisphere sources of dense water supplied to the AMOC are produced in the Arctic Mediterranean (1). Here, warm surface waters from the Atlantic flow northwards and circulate around the AM via several different pathways, gradually cooling, thereby releasing heat to the atmosphere, and becoming denser. Much of this water mass transformation is thought to occur in the Nordic Seas via intermediate and deep open ocean convection, with a smaller contribution from the Arctic that also involves the addition of dense waters from brine-2 enhanced shelf water production (1, 2). The dense water produced by these processes overflows the Greenland-Scotland Ridge (GSR), ultimately forming lower North Atlantic Deep Water (NADW), as part of the deep southward return flow of the AMOC.Because of the northward heat transfer associated with the flow of warm surface water to convection sites, changes in deep water formation in the North Atlantic and Nordic Seas are thought to be associated with the altered climate of the last glacial maximum (LGM) and the abrupt climate events of the last deglaciation (~19 to 7 thousand years ago, ka), such as the northern hemisphere cold intervals Heinrich Stadial 1 (HS1) and the Younger Dryas (YD) (3-5), which affected global climate (6,7). In this study we investigate circulation changes over the past 30 ka in the deep Norwegian Sea (and by inference, the broader AM) by reconstructing radiocarbon ventilation age and deep ocean temperature. Our results reveal an absence of deep convection within the AM throughout much of the last glacial and deglaciation and instead suggest the presence of a relatively warm and extremely poorly ventilated water mass in the glacial deep AM that subsequently overflowed southward into the North Atlantic during the deglaciation.North Atlantic radiocarbon reconstructions. Several studies...

Ice-shelf damming in the glacial Arctic Ocean: dynamical regimes of a basin-covering kilometre-thick ice shelf

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Reducing Uncertainties in Carbonate Clumped Isotope Analysis Through Consistent Carbonate‐Based Standardization

“…In Table 1 we report the δ 13 C and δ 18 O of the three gases used for establishing the reference frame (WG, CARBA, and LINDE) of the four ETH standards and of the equilibrated gases that were used in 2013 to establish the accepted values for the ETH standards reported in Meckler et al (2014). These values were subsequently used to standardize all data measured at ETH into the CDES (e.g., Meckler et al, 2015; Millan et al, 2016; Müller, Violay, et al, 2017; Thornalley et al, 2015). We also report the change in Δ 47raw (Table 1, column labeled Δ [Δ 47raw ]) obtained by using equation 10 of Daëron et al (2016) to determine the error caused by the use of the old parameters.…”

Seismic geomorphological reconstructions of Plio-Pleistocene bottom current variability at Goban Spur

“…Significant changes can be expected in terms of deep-water production within the Nordic seas, however, little evidence was found for changes in the contribution of the LSW over most of the Pleistocene (Raymo et al, 2004;Stein et al, 2006;Bell et al, 2015). In spite of the increasing number of studies that evidence strong changes in the north Atlantic water column stratification, specifically during the last climatic cycle and the past 600 ky (Thornalley et al, 2015), it is postulated here that the MOW variability is a primary driver in the Goban Spur margin evolution. Khélifi et al (2009Khélifi et al ( , 2014 documented intermittent incursions of the warm and salty MOW within the early to late Pliocene (interval ranging 130 to 165 m bsf at DSDP Site 548).…”