Abrupt deglaciation events and Holocene palaeoceanography from high‐resolution cores, Cartwright Saddle, Labrador Shelf, Canada

Abstract

The uppermost Quaternary sediments in Cartwright Saddle, Labrador Shelf, are acoustically laminated, with reflectors that can be traced over long distances. Two piston cores from the saddle record changes in sediment and meltwater delivery from the northeast margin of the Laurentide Ice Sheet (LIS) during deglaciation. Variations in sediment properties indicate a similar history of sediment accumulation over the last 12 kyr. The temporal sampling interval reaches decadal resolution in the last deglacial period 7-9 ka. Analyses of total carbonate content, sediment magnetic variables, foraminiferal species and stable isotope measurements on planktic foraminifers show that abrupt changes occurred ca. 10.9, 9.2, 8.8, 7.9 and 7 ka (with 450 yr correction). There was no distinct change in sediment character during much of the Younger Dryas chronozone. In the ␦ 18 O record, the 8.8 ka event is a dramatic Ϸ1‰ shift toward lower values, which we associate with the Noble Inlet glacial event within Hudson Strait. We do not see the pronounced low ␦ 18O event at 7.1 ka reported off Nova Scotia, but surprisingly, neither the Nova Scotia records nor other records in the Labrador Sea capture the impressive 8.8 ka change. Serious consideration must be given to the final collapse of the LIS as the cause of the 8.2 cal. ka cold event recorded in Greenland and northwest Europe.

Water isotope diffusion rates from the NorthGRIP ice core for the last 16,000 years – Glaciological and paleoclimatic implications

“…At approximately 8.5 ky b2k we observe a strong cooling event (≈ 5 K) that lasts about 500 years. Similar paleoclimatic signals indicating widespread cooler/drier conditions have been reported from regions of the North Atlantic (Andrews et al, 1999;Risebrobakken et al, 2003;Rohling and Palike, 2005) as well as monsoon areas (Gasse, 2000;Haug et al, 2001;Gupta et al, 2003;Wang et al, 2005). The magnitude and age of the event resemble those of the 8.2k event observed in the δ 18 O signal of Greenland ice cores .…”

Water isotope diffusion rates from the NorthGRIP ice core for the last 16,000 years – Glaciological and paleoclimatic implications

“…At approximately 8.5 ky b2k we observe a strong cooling event (≈ 5 K) that lasts about 500 years. Similar paleoclimatic signals indicating widespread cooler/drier conditions have been reported from regions of the North Atlantic (Andrews et al, 1999;Risebrobakken et al, 2003;Rohling and Palike, 2005) as well as monsoon areas (Gasse, 2000;Haug et al, 2001;Gupta et al, 2003;Wang et al, 2005). The magnitude and age of the event resemble those of the 8.2k event observed in the δ 18 O signal of Greenland ice cores .…”

Subglacial methanogenesis: A potential climatic amplifier?

“…We have calculated the amount of SOC in marine sediments, using an estimate of the area of marine-based ice for the Laurentide/Cordilleran/Innuitian and European ice sheets, an estimated marine sediment depth of 5 m, bulk density values of 2 g cm À3 and organic carbon contents of 0.5%. These are typical values recorded for marine sediments deposited during the Holocene in the Barents/Kara seas and on the Labrador Shelf, North America [Levitan et al, 2000;Gataullin et al, 2001;Andrews et al, 1999]. The total marine SOC for both ice sheet complexes is 29 Pg C, with 19.4 Pg of this derived from the European Ice Sheet (Table 4).…”

Linking the 8.2 ka event and its freshwater forcing in the Labrador Sea

“…[6] Our new grain size record for this core identifies an abrupt $20% increase in weight percent coarse fraction (>63 mm) dated at $8.5-8.3 ka (Figure 2b), similar to the $10% increase in the existing >125 mm record of Andrews et al [1999]. This layer lies directly above the final deglacial increase in weight percent calcite and dolomite [Andrews et al, 1999] (Figure 2b).…”

“…[6] Our new grain size record for this core identifies an abrupt $20% increase in weight percent coarse fraction (>63 mm) dated at $8.5-8.3 ka (Figure 2b), similar to the $10% increase in the existing >125 mm record of Andrews et al [1999]. This layer lies directly above the final deglacial increase in weight percent calcite and dolomite [Andrews et al, 1999] (Figure 2b). The <63 mm fraction of these layers has a reddish hue, indicative of sediment deposited during the drainage of Lake Agassiz [Andrews et al, 1995[Andrews et al, , 1999Kerwin, 1996;Barber et al, 1999].…”

Water isotope diffusion rates from the NorthGRIP ice core for the last 16,000 years – Glaciological and paleoclimatic implications

“…At approximately 8.5 ky b2k we observe a strong cooling event (≈ 5 K) that lasts about 500 years. Similar paleoclimatic signals indicating widespread cooler/drier conditions have been reported from regions of the North Atlantic (Andrews et al, 1999;Risebrobakken et al, 2003;Rohling and Palike, 2005) as well as monsoon areas (Gasse, 2000;Haug et al, 2001;Gupta et al, 2003;Wang et al, 2005). The magnitude and age of the event resemble those of the 8.2k event observed in the δ 18 O signal of Greenland ice cores .…”

Subglacial methanogenesis: A potential climatic amplifier?

“…We have calculated the amount of SOC in marine sediments, using an estimate of the area of marine-based ice for the Laurentide/Cordilleran/Innuitian and European ice sheets, an estimated marine sediment depth of 5 m, bulk density values of 2 g cm À3 and organic carbon contents of 0.5%. These are typical values recorded for marine sediments deposited during the Holocene in the Barents/Kara seas and on the Labrador Shelf, North America [Levitan et al, 2000;Gataullin et al, 2001;Andrews et al, 1999]. The total marine SOC for both ice sheet complexes is 29 Pg C, with 19.4 Pg of this derived from the European Ice Sheet (Table 4).…”

Linking the 8.2 ka event and its freshwater forcing in the Labrador Sea

“…[6] Our new grain size record for this core identifies an abrupt $20% increase in weight percent coarse fraction (>63 mm) dated at $8.5-8.3 ka (Figure 2b), similar to the $10% increase in the existing >125 mm record of Andrews et al [1999]. This layer lies directly above the final deglacial increase in weight percent calcite and dolomite [Andrews et al, 1999] (Figure 2b).…”

“…[6] Our new grain size record for this core identifies an abrupt $20% increase in weight percent coarse fraction (>63 mm) dated at $8.5-8.3 ka (Figure 2b), similar to the $10% increase in the existing >125 mm record of Andrews et al [1999]. This layer lies directly above the final deglacial increase in weight percent calcite and dolomite [Andrews et al, 1999] (Figure 2b). The <63 mm fraction of these layers has a reddish hue, indicative of sediment deposited during the drainage of Lake Agassiz [Andrews et al, 1995[Andrews et al, , 1999Kerwin, 1996;Barber et al, 1999].…”

Water isotope diffusion rates from the NorthGRIP ice core for the last 16,000 years – Glaciological and paleoclimatic implications

“…At approximately 8.5 ky b2k we observe a strong cooling event (≈ 5 K) that lasts about 500 years. Similar paleoclimatic signals indicating widespread cooler/drier conditions have been reported from regions of the North Atlantic (Andrews et al, 1999;Risebrobakken et al, 2003;Rohling and Palike, 2005) as well as monsoon areas (Gasse, 2000;Haug et al, 2001;Gupta et al, 2003;Wang et al, 2005). The magnitude and age of the event resemble those of the 8.2k event observed in the δ 18 O signal of Greenland ice cores .…”

Subglacial methanogenesis: A potential climatic amplifier?

“…We have calculated the amount of SOC in marine sediments, using an estimate of the area of marine-based ice for the Laurentide/Cordilleran/Innuitian and European ice sheets, an estimated marine sediment depth of 5 m, bulk density values of 2 g cm À3 and organic carbon contents of 0.5%. These are typical values recorded for marine sediments deposited during the Holocene in the Barents/Kara seas and on the Labrador Shelf, North America [Levitan et al, 2000;Gataullin et al, 2001;Andrews et al, 1999]. The total marine SOC for both ice sheet complexes is 29 Pg C, with 19.4 Pg of this derived from the European Ice Sheet (Table 4).…”

Linking the 8.2 ka event and its freshwater forcing in the Labrador Sea

“…[6] Our new grain size record for this core identifies an abrupt $20% increase in weight percent coarse fraction (>63 mm) dated at $8.5-8.3 ka (Figure 2b), similar to the $10% increase in the existing >125 mm record of Andrews et al [1999]. This layer lies directly above the final deglacial increase in weight percent calcite and dolomite [Andrews et al, 1999] (Figure 2b).…”

“…[6] Our new grain size record for this core identifies an abrupt $20% increase in weight percent coarse fraction (>63 mm) dated at $8.5-8.3 ka (Figure 2b), similar to the $10% increase in the existing >125 mm record of Andrews et al [1999]. This layer lies directly above the final deglacial increase in weight percent calcite and dolomite [Andrews et al, 1999] (Figure 2b). The <63 mm fraction of these layers has a reddish hue, indicative of sediment deposited during the drainage of Lake Agassiz [Andrews et al, 1995[Andrews et al, , 1999Kerwin, 1996;Barber et al, 1999].…”