Response of the North Atlantic surface and intermediate ocean structure to climate warming of MIS 11

Abstract

Investigating past interglacial climates not only help to understand how the climate system operates in general, it also forms a vital basis for climate predictions. We reconstructed vertical stratification changes in temperature and salinity in the North Atlantic for a period some 400 ka ago (MIS11), an interglacial time analogue of a future climate. As inferred from a unique set of biogeochemical, geochemical, and faunal data, the internal upper ocean stratification across MIS 11 shows distinct depth-dependent dynamical changes related to vertical as well as lateral shifts in the upper Atlantic meridional circulation system. Importantly, transient cold events are recognized near the end of the long phase of postglacial warming at surface, subsurface, mid, and deeper water layers. These data demonstrate that MIS 11 coolings over the North Atlantic were initially triggered by freshwater input at the surface and expansion of cold polar waters into the Subpolar Gyre. The cooling signal was then transmitted downwards into mid-water depths. Since the cold events occurred after the main deglacial phase we suggest that their cause might be related to continuous melting of the Greenland ice sheet, a mechanism that might also be relevant for the present and upcoming climate.

Interglacial Paleoclimate in the Arctic

“…McManus et al (1999) first showed at ODP Site 980 in the subpolar North Atlantic Ocean that significant suborbital variability over the last 500 ka occurred when ice sheets reached a critical size. This variability was later confirmed by Helmke and Bauch (2003), , and Kandiano et al (2016) for the Nordic seas and in midlatitudes of the northeast North Atlantic by Voelker et al (2010), Rodrigues et al (2011), Doherty and Thibodeau (2018), and Kandiano et al (2017). Figure 4 shows several of these proxy records for the period MIS 12 through MIS 10 (450 to 350 ka) going from north (top, panel 4a) to south (bottom, panel 4j).…”

“…Taken together, these records show that suborbital variability linked to glacial processes and ocean circulation were fundamental features both during Termination V and the MIS 11‐10 transition in regions of the Nordic seas and North Atlantic. Transient suborbital cold events during Termination V were likely triggered by freshwater influx from melting ice, perhaps the Greenland Ice Sheet, and they affected surface, middepth, and deeper water layers as well as the AMOC (Kandiano et al, ). Similarly, during the transition into the MIS 10 glacial starting about 395 ka, there were multiple cool/warm cycles reflecting a weakening AMOC similar to those seen in HE during the MIS 5a‐MIS 3 interval (Voelker et al, ).…”

Microbial Production of Conjugated Linoleic Acid and Conjugated Linolenic Acid Relies on a Multienzymatic System

“…This hypothesis seems to be supported by investigations performed with other organisms: for example, the cis-12 linoleate isomerase (LAI) gene of Fusarium graminearum (FgLAI12), responsible for the conversion of LA into RA, was characterized (32). Assays of gene deletion mutants showed, among other effects, a reduction of mycelial growth.…”

A High‐Resolution Speleothem Record of Marine Isotope Stage 11 as a Natural Analog to Holocene Asian Summer Monsoon Variations

“…Two additional abrupt cold events have also been recognized in MIS 11 by a high-resolution lacustrine record from North Asia (Prokopenko et al, 2010). Furthermore, a temperature record from the North Atlantic (Kandiano et al, 2017) Figures 4 and S9). Notably, the YXEs show average pacing of~1.4 Kyr and amplitude of~0.8‰ (Table S3 and Figure S9), which broadly resembles the Holocene WMEs inferred by the counterpart cave records (Dykoski et al, 2005;Wang, 2005).…”