Constraints on the Northwestern Atlantic Deep Water Circulation From ²³¹Pa/²³⁰Th During the Last 30,000 Years

Abstract

Global climatic changes during the last glacial and deglacial have been related to variations of the Atlantic Meridional Overturning Circulation (AMOC). Here, we present new and refined 231 Pa/ 230 Th down-core profiles extending back to 30 ka BP from the northwestern Atlantic along the Atlantic Deep Western Boundary Current, which is the main component of the southward deep backflow of the AMOC. Besides the well-known Bermuda Rise records, available high-resolution 231 Pa/ 230 Th data in the northwestern Atlantic are still sparse. Our new records along with reconstructions of deep water provenance from Nd isotopes constrain the timing and magnitude of past changes in AMOC from an additional northwestern Atlantic region forming a depth transect between 3,000-and 4,760-m water depth. Our extended and improved data set confirms the weakening of the AMOC during deglacial cold spells such as Heinrich Event 1 and the Younger Dryas interrupted by a reinvigoration during the Bølling-Allerød interstadial as seen in the prominent 231 Pa/ 230 Th records from the Bermuda Rise. However, in contrast to the Bermuda Rise records, we find a clearly reduced circulation strength during the Last Glacial Maximum in the deep Atlantic.

Multi-proxy constraints on Atlantic circulation dynamics since the last ice age

“…Evidence for little change in water mass provenance also comes from εNd, reconstructions of which also exhibit only moderate changes from the LGM to HS1 26,34 . The notion of a full AMOC collapse was previously underscored by a Pa/Th record of the deep Northwest Atlantic 5 , yet the same magnitude of the HS1 excursion did not emerge as a fully coherent pattern in Pa/ Th records throughout the Atlantic, with most time series indicating smaller changes from the LGM to HS1 12,[35][36][37] as suggested here by our multi-proxy approach. As such, local particle effects could have influenced Pa/Th in the Northwest Atlantic 36,38 , which has major ramifications on the Bermuda Rise time series, which is often considered as a benchmark AMOC record.…”

“…The notion of a full AMOC collapse was previously underscored by a Pa/Th record of the deep Northwest Atlantic 5 , yet the same magnitude of the HS1 excursion did not emerge as a fully coherent pattern in Pa/Th records throughout the Atlantic, with most time series indicating smaller changes from the LGM to HS1 12 , 35 – 37 as suggested here by our multi-proxy approach. As such, local particle effects could have influenced Pa/Th in the Northwest Atlantic 36 , 38 , which has major ramifications on the Bermuda Rise time series, which is often considered as a benchmark AMOC record. Our assessment therefore implies that throughout the early deglaciation, SSW occupied a larger fraction of the Atlantic than did water ventilated from the north, which however was never fully replaced as its Atlantic fraction never dropped below 20%.…”

The deglaciation of Upernavik trough, West Greenland, and its Holocene sediment infill: processes and provenance

“…2018, 2019; Süfke et al . 2019; Xu et al . 2021) and modelled (Obase & Abe‐Ouchi 2019) throughout the western North Atlantic, providing a probable driver for such an enhanced northward advection of Atlantic Waters to Baffin Bay via the WGC.…”

“…An analogous scenario has been proposed for the southerly adjacent Uummannaq and Disko troughs by Jennings et al (2017), who also invoked subsurface warming (Marcott et al 2011) and advection of Atlantic waters (Knutz et al 2011) as a driving force for initial melt of grounded ice on the outer shelf. A large-scale invigoration of the AMOC during the B/A was recorded (McManus et al 2004;Lippold et al 2012Lippold et al , 2019P€ oppelmeier et al 2018S€ ufke et al 2019;Xu et al 2021) and modelled (Obase & Abe-Ouchi 2019) throughout the western North Atlantic, providing a probable driver for such an enhanced northward advection of Atlantic Waters to Baffin Bay via the WGC. Our results indicate that the effects of this invigoration have reached at least as far north as the Upernavik trough.…”

Millennial-scale variability in eastern South American climate and western South Atlantic circulation during the last 70,000 years

“…Proxies of water mass residence time and flow rates should confirm this scenario. In fact, 14 C-depleted values (CHEN et al, 2015;LUND et al, 2015;ROBINSON et al, 2005;THORNALLEY et al, 2011) and high sedimentary 231 Pa/ 230 Th (HENRY et al, 2016;MCMANUS et al, 2004;MULITZA et al, 2017;SÜFKE et al, 2019) (Fig. 5.3b, c) from the western Atlantic suggest a reduced ventilation at NCW depths coeval with fresh water input into the high latitudes of the North Atlantic (marked by pulses of ice-rafted debris -IRD; Fig.…”