South Atlantic intermediate water advances into the North‐east Atlantic with reduced Atlantic meridional overturning circulation during the last glacial period

Abstract

The Nd isotopic composition (eNd) of seawater and cold-water coral (CWC) samples from the Gulf of C adiz and the Alboran Sea, at a depth of 280-827 m were investigated in order to constrain middepth water mass dynamics within the Gulf of C adiz over the past 40 ka. eNd of glacial and Holocene CWC from the Alboran Sea and the northern Gulf of C adiz reveals relatively constant values (28.6 to 29.0 and 29.5 to 210.4, respectively). Such values are similar to those of the surrounding present-day middepth waters from the Mediterranean Outflow Water (MOW; eNd 29.4) and Mediterranean Sea Water (MSW; eNd 29.9). In contrast, glacial eNd values for CWC collected at thermocline depth (550-827 m) in the southern Gulf of C adiz display a higher average value (28.9 6 0.4) compared to the present-day value (211.7 6 0.3). This implies a higher relative contribution of water masses of Mediterranean (MSW) or South Atlantic origin (East Antarctic Intermediate Water, EAAIW). Our study has produced the first evidence of significant radiogenic eNd values ( 28) at 19, 23-24, and 27 ka, which are coeval with increasing iceberg discharges and a weakening of Atlantic Meridional Overturning Circulation (AMOC). Since MOW eNd values remained stable during the last glacial period, it is suggested that these radiogenic eNd values most likely reflect an enhanced northward propagation of glacial EAAIW into the eastern Atlantic Basin.

Transient hydrodynamic effects influence organic carbon signatures in marine sediments

“…Increasing grain-sizes 42 and increases in reworked nannofossil influx 11 , 55 (Fig. 3d ) during deglacial transitions and the mid-Holocene correspond to intervals of decreased Nile river discharge 56 , which led to more saline (denser) MOW 41 , 45 , 50 , and decreased formation of less dense, cold NADW 54 , 57 . Intervals associated with cold Arctic conditions 2 , 54 , 56 show decreased percent total OC (TOC % [Fig.…”

Changes in Intermediate Circulation in the Bay of Bengal Since the Last Glacial Maximum as Inferred From Benthic Foraminifera Assemblages and Geochemical Proxies

“…The role of AAIW is still controversial during the last deglaciation in the Atlantic Ocean, several studies suggesting a reduced northward flux of AAIW into the tropical Atlantic (e.g., Came et al, 2008;Gu et al, 2017;Howe et al, 2016;Xie et al, 2012). However, other studies indicate an increased penetration of AAIW in the Atlantic Ocean (e.g., Dubois-Dauphin et al, 2016;Pahnke et al, 2008;Poggemann et al, 2017Poggemann et al, , 2018. This is also strongly supported by the intermediate records of benthic carbon isotope, ɛ Nd , and B-P age offsets from the North Indian (Bryan et al, 2010;Jung et al, 2009;Yu et al, 2018), and Pacific Ocean (e.g., Bostock et al, 2010;Mix et al, 1991;Pahnke & Zahn, 2005).…”

“…Previous studies of the intermediate water circulation during the last glaciation have mainly focused on the Atlantic Ocean (e.g., Lynch-Stieglitz et al, 2007;Oppo & Fairbanks, 1987;Pahnke et al, 2008) and the Pacific Ocean (e.g., Bostock et al, 2010;Mix et al, 1991;Pahnke & Zahn, 2005). These studies suggest an increased northward penetration of Antarctic Intermediate Water (AAIW) into the Pacific and Atlantic Oceans during glacial periods, as well as at a millennial time scale during the Heinrich events and stadials (e.g., Cao et al, 2007;Dubois-Dauphin et al, 2016;Pahnke et al, 2008;Pahnke & Zahn, 2005). In contrast, several studies based on ɛ Nd and Cd/Ca records (e.g., Came et al, 2008;Gu et al, 2017;Howe et al, 2016;Xie et al, 2012) suggest that no changes occurred or even that there was decreased northward penetration of AAIW during HS1 and the Younger Dryas.…”

The large-scale evolution of neodymium isotopic composition in the global modern and Holocene ocean revealed from seawater and archive data

“…The seawater Nd database of Lacan et al (2012) has been updated by integrating all seawater  Nd data published up to September 2016 to our knowledge ( Figure 1) (Bayon et al, 2011;Grenier et al, 2011;Carter et al, 2012;Grasse et al, 2012;Singh et al, 2012;Amakawa et al, 2013;Chen et al, 2013b;Ehlert et al, 2013;Jeandel et al, 2013;Freslon et al, 2014;Garcia-Solsona et al, 2014;Goswami et al, 2014;Haley et al, 2014;Huang et al, 2014;Werner et al, 2014;Abbott et al, 2015;Basak et al, 2015;Stichel et al, 2015;Wu et al, 2015a;Du et al, 2016;Dubois-Dauphin et al, 2016a;Fröllje et al, 2016;Lambelet et al, 2016;Dubois-Dauphin et al, submitted). Following the approach of the previous compilation (Lacan et al, 2012), we focus on seawater Nd isotopic compositions.…”