Millennial-Scale Interaction between Ice Sheets and Ocean Circulation during Marine Isotope Stage 100

Abstract

Waxing/waning of the ice sheets and the associated change in thermohaline circulation have played an important role in global climate change since major continental ice sheets appeared in the northern hemisphere about 2.75 million years ago. In the earliest glacial stages, however, establishment of the linkage between ice sheet development and ocean circulation remains largely unclear. Here, we show new high-resolution records of marine isotope stage 100 recovered from deep-sea sediments on the Gardar Drift, in the subpolar North Atlantic. Results of a wide range of analyses clearly reveal the influence of millennial-scale variability in iceberg discharge on ocean surface condition and bottom current variability in the subpolar North Atlantic during marine isotope stage 100. We identified eight events of ice-rafted debris, which occurred mostly with decreases in sea surface temperature and in current components indicating North Atlantic Deep Water. These decreases are interpreted by weakened deep water formation linked to iceberg discharge, similarly to observations from the last glacial period. Dolomite fraction of the ice-rafted events in early MIS 100 like the last glacial Heinrich events suggests massive collapse of the Laurentide ice sheet in North America. At the same time, our early glacial data suggest differences from the last glacial period: absence of 1470-year periodicity in the interactions between ice sheets and ocean, and northerly shift of the ice-rafted debris belt. Our high-resolution data largely improve the picture of ice-sheet/ocean interactions on millennial time scales in the early glacial period after major Northern Hemisphere glaciation.

Latest Pliocene Northern Hemisphere glaciation amplified by intensified Atlantic meridional overturning circulation

“…1) (see "Methods" section). This site is well suited to reconstruct ice sheet-ocean interaction, including the AMOC, because of its location under the strong influence of icebergs 21,22 , the Irminger Current (north-western branch of the NAC), and the Iceland-Scotland Overflow Water (ISOW). Currently, two kinds of cold, dense waters pass southward across the Greenland-Scotland Ridge as overflows: the ISOW to the east and Denmark Strait Overflow Water (DSOW) to the west (Fig.…”

“…The MIS G4, G2, and 104 glacials each experienced a single prominent iceberg event (Fig. 2), in contrast to the MIS 100 glacial when icebergs repeatedly arrived on millennial time scales 22 . The scale of the individual iceberg events decreased step by step after the largest one in MIS G4.…”

“…2l). On the other hand, concentrations of alkenone, calcite (reflecting nannofossil abundance 22 ), and diatoms decreased during glacials ( Fig. 2i-k), indicating decreases in surface water productivity.…”

“…Previous rock-magnetic studies based on the IRM acquisition curves, S-ratios, and low-temperature and high-temperature magnetometry (ref. 22 and references therein) revealed that the dominant magnetic mineral of the Site U1314 sediments was magnetite. The coercivity of a magnetic mineral varies with the mineral's properties, such as the chemical composition, grain size, grain shape, and stress.…”

“…The IRM acquisition curves were measured for the samples at 2-cm intervals between 269. 13 22 ) were used for calculations, but the samples with the highest IRD fractions (267.95 and 267.93 mcd) were excluded from analysis because of their weak magnetic signals. The IRM acquisition curves were obtained by the application of stepwiseincreasing uniaxial fields to the samples with 29 steps from 1 mT to 1 T, using a MicroMag 2900 Alternating Gradient Magnetometer (Princeton Measurement Corporation).…”