Vulnerability of the Cordilleran Ice Sheet to iceberg calving during late Quaternary rapid climate change events

Abstract

[1] We present the first high-resolution record of iceberg calving on the continental slope of Vancouver Island, British Columbia (MD02-2496, 48°58N, 127°02W, 1243 m water depth), through the last glacial from the Cordilleran Ice Sheet (CIS). These previously unknown ice-rafted debris (IRD) events representing significant retreat of the western margin of the CIS out of marine waters show little correspondence with local climate change. High-resolution radiocarbon dating indicates that the younger IRD events coincide with global radiocarbon age plateaus that allow direct correlation with distal climate records where the same plateaus have been identified. The coincidence of episodic shedding of IRD from the CIS with North Atlantic climate events (i.e., North Atlantic Deep Water shutdown, and Heinrich events) begs the question: What drove CIS destabilization? Forcing appears to be external to CIS dynamics perhaps resulting from either eustatic sea level rise or episodes of atmospheric warming over the North American continent.Citation: Hendy, I. L., and T. Cosma (2008), Vulnerability of the Cordilleran Ice Sheet to iceberg calving during late Quaternary rapid climate change events, Paleoceanography, 23, PA2101,

Deglacial ocean warming and marine margin retreat of the Cordilleran Ice Sheet in the North Pacific Ocean

“…4B; Hendy and Cosma, 2008). During this interval the number of >250 μm grains g −1 increased from a background of <1 to a maximum of >500 grains g −1 at 16.3 ka, abruptly ending at 16.1 ka.…”

“…3A. The N. pachyderma δ 18 O calcite record has been presented previously in Hendy and Cosma (2008). In comparison to temperature reconstructions of the planktonic foraminifera at MD02-2496, the δ 18 O calcite values display less variability (Fig.…”

The role of the cryosphere in source-to-sink systems

“…In Antarctica, IRD concentrations in open marine sediments do not appear to be related to ice sheet dynamics, but rather reflect relative winnowing of fines by strong bottom currents (Cofaigh et al, 2001b;Cofaigh, 2012) and other deepwater sediment reworking processes over the past million years. In temperate glacial settings, higher concentrations of IRD have been associated with ice margin retreat on continental shelves (Hendy and Cosma, 2008), but may also reflect seasonally varying suspended-sediment concentrations in fjords . Regional oceanography can also have a major impact on IRD dispersal patterns, varying greatly over short distances (Solheim et al, 1998).…”

“…13; Barrie et al, 1991;Hendy and Cosma, 2008;Davies et al, 2011;Lekens et al, 2005;Vorren et al, 1998). Higher glacigenic sediment fluxes during the initial deglacial period are recognized both in terms of 14 C-or δ 18 O-established chronologies and also from lithofacies proxies (e.g., laminated glacimarine mud).…”

Ironing out carbon export to the deep ocean

“…Consequently, an additional explanation for increased large diatom abundance during deglaciation is that significant quantities of fresh glacial sediment were delivered to the Northeast Pacific Ocean. Deglaciation began in the Northeast Pacific at 17,200 y BP as the regional Cordilleran Ice Sheet began to retreat rapidly (13), first releasing icebergs (14) and then fine-grained rock flour through outwash as the retreating ice sheet uncovered freshly eroded rock material (13). This addition of glacial sediment occurred 675 km upstream in the California Current (13,15) How global climate change will affect the carbon cycle via biological pump efficiency is directly relevant today and for the future.…”