A micropalaeontological perspective on export productivity, oxygenation and temperature in NE Atlantic deep-waters across Terminations I and II

Abstract

A micropalaeontological perspective on export productivity, oxygenation and temperature in NE Atlantic deep-waters across Terminations I and II, Global and Planetary Change (2015), AbstractCensus counts of benthic foraminifera were studied from the SW Iberian Margin to reconstruct past changes in deep-water hydrography across Terminations I and II. Detailed benthic faunal data (> 125 µm size-fraction) allow us to evaluate the limitations imposed by taphonomic processes and restricted size-fractions. The comparison of recent (mudline) and fossil assemblages at IODP Site U1385 indicates the quick post-mortem disintegration of shells of astrorhizoid taxa (~80% of the present-day fauna), resulting in impoverished fossil assemblages. While the application of quantitative proxy methods is problematic under these circumstances, the fossil assemblages can still provide a qualitative palaeoenvironmental signal that, while most fully expressed in the 125-212 µm size-fraction, is nonetheless also expressed to some degree in the > 212 µm size-fraction.Variations in the benthic foraminiferal assemblages reveal information about changing organic matter supply, deep-water oxygenation and temperature. MIS 2 is generally characterized by an elevated trophic state and variable oxic conditions, with oxygenation minima culminating in the Younger Dryas (YD) and Heinrich Stadials (HS) 1, 2 and 3. Low oxic conditions coincide with decreased water-temperature and lower benthic δ 13 C, pointing to the strong influence of a southern sourced water-mass during these periods. HS 1 is the most extreme of these intervals, providing further evidence for a severe temporary reduction or even shutdown of ACCEPTED MANUSCRIPT 2 AMOC. With the inception of MIS 1, organic matter supply reduced and a better ventilated deep-water environment bathed by NEADW is established.For Termination II, clear indications of southern-sourced water are limited to the early phase of HS 11. During the latter part of HS 11, the deep-water environment seems to be determined by strongly increased supply of organic matter, potentially explaining the decoupling of benthic δ 13 C and Mg/Ca records of earlier studies as a phytodetritus effect on the carbon isotope signal. However, the presence of a warm, nutrient-rich and poorly oxygenated water-mass cannot be ruled out. With the inception of interglacial MIS 5e trophic conditions are reduced and ventilation by NEADW increases.

Palaeoceanographic and palaeoclimatic changes during the last 37,000 years detected in the SE Bay of Biscay based on benthic foraminifera

“…The reduction of deep-water formation produced the accumulation of OM in the hypoxic marine bottom (Loncaric et al, 1998). The results based on benthic foraminifera from core PP10-12 support those by Grunert et al (2015) of the temporal slowdown or even total shutdown of the AMOC during H1 event.…”

“…In the classification of Kaiho, 1994 it is considered as dyxosic species that can stand anoxic conditions (Geslin et al, 2004;Fontanier et al, 2002). Thus it is a useful proxy to detect levels of extremely low oxygen rates (Schonfeld, 2001;Jorissen et al, 2007;Grunert et al, 2015). It occurs during H4 in Portugal (Baas et al, 1998), as well as in H1 and H4 with maxima IRD in Bay of Biscay (Loncaric et al, 1998).…”

“…These works, located from shelf to bathyal profiles, described benthic foraminifera assemblages controlled by parameters as organic carbon flux to the marine benthos, bottom currents and grain size, oxygen content and carbonate saturation of sediments (Mackensen et al, 1995;Jorissen et al, 2007). The distribution of living benthic foraminifera assemblages have been used as proxies of the response of benthic ecosystems to atmospheric changes and rapid climatic changes in the North Atlantic Rasmussen et al, 2002;Grunert et al, 2015) among others. In the Bay of Biscay Martínez- described climatic events from the MIS 3 to the Holocene registered in the Basque shelf, however from H1 to Holocene were scarcely recorded due to various sedimentary hiatuses.…”

Impact of bottom water currents on benthic foraminiferal assemblages in a cold-water coral environment: The Moira Mounds (NE Atlantic)

“…Furthermore, Grunert et al (2015) observed higher abundances of C. teretis during the Last Glacial Maximum along the southwest Iberian Margin. These matching observations from different authors (Rüggeberg et al, 2007;Schönfeld et al, 2011;Morigi et al, 2012;Grunert et al, 2015) could confirm that most dominant species in the DA at the dMM (e.g. Elphidium spp., C. kullenbergi, C. teretis, C. crassa and S. schlumbergeri) are part of a reworked glacial fauna.…”

Sea-Air CO2 Exchange in the SW Iberian Upwelling System during Two Contrasting Climate Cycles: 860–780 ka and 630–520 ka

“…In this scenario, the benthic community is not able to consume all of it and storage of organic carbon occurs [28]. Therefore, if a high amount of organic carbon reaches the poorly ventilated bottom, it will result in the impoverishment of the benthic habitat [54,55], and in the enhancement of carbon sequestration. This is probably what happened during 803 and 798 ka (Figure 3b,d).…”