Ice sheet sources of sea level rise and freshwater discharge during the last deglaciation

Abstract

We review and synthesize the geologic record that constrains the sources of sea level rise and freshwater discharge to the global oceans associated with retreat of ice sheets during the last deglaciation. The Last Glacial Maximum (∼26–19 ka) was terminated by a rapid 5–10 m sea level rise at 19.0–19.5 ka, sourced largely from Northern Hemisphere ice sheet retreat in response to high northern latitude insolation forcing. Sea level rise of 8–20 m from ∼19 to 14.5 ka can be attributed to continued retreat of the Laurentide and Eurasian Ice Sheets, with an additional freshwater forcing of uncertain amount delivered by Heinrich event 1. The source of the abrupt acceleration in sea level rise at ∼14.6 ka (meltwater pulse 1A, ∼14–15 m) includes contributions of 6.5–10 m from Northern Hemisphere ice sheets, of which 2–7 m represents an excess contribution above that derived from ongoing ice sheet retreat. Widespread retreat of Antarctic ice sheets began at 14.0–15.0 ka, which, together with geophysical modeling of far‐field sea level records, suggests an Antarctic contribution to this meltwater pulse as well. The cause of the subsequent Younger Dryas cold event can be attributed to eastward freshwater runoff from the Lake Agassiz basin to the St. Lawrence estuary that agrees with existing Lake Agassiz outlet radiocarbon dates. Much of the early Holocene sea level rise can be explained by Laurentide and Scandinavian Ice Sheet retreat, with collapse of Laurentide ice over Hudson Bay and drainage of Lake Agassiz basin runoff at ∼8.4–8.2 ka to the Labrador Sea causing the 8.2 ka event.

Oxygen isotope geochemistry of Laurentide ice-sheet meltwater across Termination I

“…S-6eS-10). These intervals encompass the period of most rapid sea-level rise through the last deglaciation (Carlson and Clark, 2012). The linear relationships in each of the core intervals from 15.5 to 13.4 ka display clear mixing between open-ocean Gulf of Mexico seawater and LIS meltwater.…”

“…The evolution and demise of continental ice sheets is intrinsically linked to variations in sea level (Carlson and Clark, 2012;Deschamps et al, 2012;Gregoire et al, 2012;Lambeck et al, 2002) and ocean circulation (Clark et al, 2001;Thornalley et al, 2010) on glacial/interglacial timescales. Numerical models provide insight into the spatial and temporal patterns of the history of continental ice sheets such as the Laurentide Ice Sheet (LIS) during the last glacial cycle.…”

On the reconstruction of palaeo-ice sheets: Recent advances and future challenges

“…Opinions differ about precise timing and routing of GLA overflow during the YD, because different approaches often yield different interpretations (e.g. deVernal et al, 1996;Tarasov and Peltier, 2005;Carlson et al, 2007;Murton et al, 2010;Not and Hillaire-Marcel, 2012;Cronin et al, 2012;Carlson and Clark, 2012). In a recent review, Carlson and Clark (2012) favoured an easterly route, but numerical modelling suggests a large influx of freshwater into the Arctic Ocean was more likely (although not necessarily from GLA: Tarasov and Peltier, 2005), and would have had a more significant impact on ocean circulation (Condron and Winsor, 2012).…”

“…deVernal et al, 1996;Tarasov and Peltier, 2005;Carlson et al, 2007;Murton et al, 2010;Not and Hillaire-Marcel, 2012;Cronin et al, 2012;Carlson and Clark, 2012). In a recent review, Carlson and Clark (2012) favoured an easterly route, but numerical modelling suggests a large influx of freshwater into the Arctic Ocean was more likely (although not necessarily from GLA: Tarasov and Peltier, 2005), and would have had a more significant impact on ocean circulation (Condron and Winsor, 2012). Several studies of deep-sea Arctic oxygen isotopes , faunal assemblages , Taldenkova et al, 2013, and other proxies (reviewed in Carlson and Clark, 2012) provide evidence for significant meltwater discharge through the Mackenzie River at the onset of the YD (see also Section 2.6), as does an OSL-dated sequence at the mouth of the Mackenzie River (Murton et al, 2010).…”

Relative sea-level data from southwest Scotland constrain meltwater-driven sea-level jumps prior to the 8.2 kyr BP event

“…The relatively large and abrupt freshwater pulses at ~8700 and ~8560 cal yr BP 765 associated with the opening of the Tyrrell Sea and first drainage of LAO respectively could 766 have preconditioned the AMOC (e.g. Carlson and Clark, 2012), with a relatively modest 767 freshwater perturbation at ~8270 yrs BP triggering its eventual reorganization. Thereafter, it 768 is possible that sea-ice-albedo feedbacks (Wiersma and Jongma, 2010;Otto-Bliesner and Brady, 2010) and freshwater fluxes were important in forcing the 8.2 event (Teller et al,770 2002; Törnqvist and Hijma, 2012 hypotheses that lie at the heart of this study.…”