Anatomy of Heinrich Layer 1 and its role in the last deglaciation

Abstract

X‐ray fluorescence (XRF) core scanning and X‐ray computed tomography data were measured every 1 mm to study the structure of Heinrich Event 1 during the last deglaciation at International Ocean Discovery Program Site U1308. Heinrich Layer 1 comprises two distinct layers of ice‐rafted detritus (IRD), which are rich in detrital carbonate (DC) and poor in foraminifera. Each DC layer consists of poorly sorted, coarse‐grained clasts of IRD embedded in a dense, fine‐grained matrix of glacial rock flour that is partially cemented. The radiocarbon ages of foraminifera at the base of the two layers indicate a difference of 1400 14C years, suggesting that they are two distinct events, but the calendar ages depend upon assumptions made for surface reservoir ages. The double peak indicates at least two distinct stages of discharge of the ice streams that drained the Laurentide Ice Sheet through Hudson Strait during HE1 or, alternatively, the discharge of two independent ice streams containing detrital carbonate. Heinrich Event 1.1 was the larger of the two events and began at ~16.2 ka (15.5–17.1 ka) when the polar North Atlantic was already cold and Atlantic Meridional Overturning Circulation (AMOC) weakened. The younger peak (H1.2) at ~15.1 ka (14.3 to 15.9 ka) was a weaker event than H1.1 that was accompanied by minor cooling. Our results support a complex history for Heinrich Stadial 1 (HS1) with reduction in AMOC during the early part (~20–16.2 ka) possibly driven by melting of European ice sheets, whereas the Laurentide Ice Sheet assumed a greater role during the latter half (~16.2–14.7 ka).

Timing of Deglacial AMOC Variability From a High‐Resolution Seawater Cadmium Reconstruction

“…An obvious indication of the resumption of upper AMOC and its associated northward heat transport would be a temperature increase in North Atlantic surface waters. Indeed, this is indicated near 16 ka in several sea surface temperature proxy records from the subpolar North Atlantic (Bond et al, ; Hodell et al, ; Naafs et al, ).…”

A Saltier Glacial Mediterranean Outflow

“…(c) Age model (meters composite depth (mcd) scale) at Site U1390 (Table ) with the yellow circles and black marks representing the visual tie points and 14 C dates, respectively. Age ranges: S1; 9.8–5.7 kyr cal BP (De Lange et al, ), YD; 12.7–11.7 kyr cal BP, Bølling‐Allerød (B/A); 14.7–12.9 kyr cal BP (Steffensen et al, ) and HS1; 18–14.3 kyr cal BP with H1.1; 17.1–15.5 kyr cal BP and H1.2; 15.9–14.3 kyr cal BP (Hodell et al, ).…”

Stability of the Atlantic Meridional Overturning Circulation: A Review and Synthesis

“…It was accompanied by an early external freshwater input (Chen et al, 2016;Ménot et al, 2006) mostly likely from Eurasian ice sheets (Grousset et al, 2001;Ng et al, 2018;Peck et al, 2006). As a second step, an off state persisted for quite a few hundreds to a thousand years, with substantial ice rafting events from the LIS (Heinrich events) as a consequence (Barker et al, 2015;Hodell et al, 2017;Marcott et al, 2011).…”