Holocene climate change in the Ross Sea region (RS)

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This page is part of the topic Regional patterns of holocene climate change in Antarctica

Deglaciation history the Pleistocene-Holocene transition

3.28 Selected Holocene environmental changes – Ross Sea

A grounded ice sheet fed from the Ross Embayment filled McMurdo Sound at the LGM and remained at its LGM position until c. 12.7 14C ka BP (c. 14.7-15.2 ka BP). The following ice recession was slow until c. 10.8 14C ka BP (c. 12.7-12.9 ka BP) (Denton and Marchant, 2000[1]; Hall and Denton, 2000[2]) (Figure 3.28). The Piedmont Glacier was probably also at its LGM position at c. 10.7 14C ka BP (c. 12.6-12.8 ka BP) (Hall and Denton, 2000[2]). The grounded ice sheet blocked several valleys in the McMurdo Dry Valleys and fed large proglacial lakes such as Lake Washburn and Lake Wright, which had water over 500 m deep in some valleys (Hall and Denton, 1995[3]) and existed until the early Holocene (Hall et al., 2000[4]; Hendy, 2000[5]; Hall et al., 2001[6]). The large amount of water in these lakes was probably derived from melting glaciers as a result of dry and cold conditions, which led to decreased snowfall and lower albedo values (Hall and Denton, 2002[7]). Between c. 14 ka and 8 ka BP these large proglacial lakes started to evaporate (Hendy, 2000[5]); the evaporation of Lake Washburn started during the LGM. Lake level lowering was discontinuous, with a series of high and low stands (Wagner et al., 2006[8]). Significant changes evident in the geochemistry of a sediment core from Lake Fryxell between c. 13.5 and 11 ka BP suggest a further desiccation event at the Pleistocene-Holocene transition (Wagner et al., 2006[8]).

After the early Holocene

The last remnants of grounded ice in Taylor Valley post-date c. 8.4 14C ka BP (c. 9-9.4 ka BP), and penguins did not recolonize the RS region until c. 8 ka BP, after an absence of c. 19 Ka (Hall et al., 2006[9]; Emslie et al., 2007[10]). The period from c. 8 ka BP shows some discrepancies. Evidence from relict deltas for an increase in the moisture supply at c. 6 14C ka BP (c. 6.8 ka BP, Hall et al., 2000[4])) contrasts with evidence for increased salinity between c. 9 and 4 ka BP in a sediment core from Lake Fryxell (Wagner et al., 2006[8]). This discrepancy could be explained by dating uncertainties or the relict deltas being from smaller local lakes (Wagner et al., 2006[8]).

3.17 Sea ice distribution at the Southern Ocean EPILOG-LGM (E-LGM) time slice. E-LGM-winter sea ice (E-LGM-WSI) indicates maximum extent of winter sea ice (September concentration >15%). Modern winter sea ice (M-WSI) shows extent of >15% September sea ice concentration according to Comiso et al. (2003[11]). Values indicate estimated winter (September) sea ice concentration in percent derived with Modern Analog Techniques and Generalized Additive Models. Signature legend: (1) concomitant occurrence of cold-water indicator diatom F. obliquecostata (>1% of diatom assemblage) and summer sea ice (February concentration >0%) interpreted to represent sporadic occurrence of ELGM summer sea ice; (2) presence of WSI (September concentration >15%, diatom WSI indicators >1%); (3) no WSI (September concentration <15%, diatom WSI indicators <1%) (Gersonde et al., 2005[12])

The presence of hairs from Southern Elephant Seals along with the remains of Adélie Penguins between c. 6 and 4 14C ka BP, indicates less sea ice than today, but sufficient pack ice for penguins to forage during spring (Emslie et al., 2007[10]). The final retreat of the Ross Ice Sheet and deglaciation is estimated to have occurred around that time; c. 5.4 14C ka BP (c. 6.3 - 5.9 ka BP, Hall and Denton, 2000[2]), coincident with the start of the recession of parts of the Wilson Piedmont Glacier at c. 5.5 14C ka BP (c. 6.4-6.27 ka BP) that lasted until at least c. 4.4-3.1 14C ka BP (c. 5.2-4.8 - 3.5-3.3 ka BP, Hall and Denton, 2000[2])). This corresponds with a secondary climate optimum detected in the ice cores of the RS sector, between 7 and 5 ka BP (Masson et al., 2000[13]), and at Siple Dome c 5.2 ka (Figure 3.17).

The Mid Holocene

In Lake Fryxell well-developed microbial mats occurred from c. 4 ka BP onwards, which indicates similar environmental conditions and water depths to those found today (Wagner et al., 2006[8]). Between c. 4 and 2.3 14C ka BP (c. 4.8-4.4 and 2.6-2.3 ka BP) elephant seals are completely absent from the region, whereas the Adélie Penguin population increased between c. 4 and 3 ka BP (Baroni and Orombelli, 1994[14]; Emslie and Woehler, 2005[15]). These data suggest that there was sufficient pack ice, but less than today, implying that conditions were relatively warm (Hall et al., 2006[9]). This so-called ‘penguin optimum’ was followed by a period of high lake levels between c. 3 and 2 14C ka BP (c. 3.3-2.9 and 2-1.7 ka BP) in water bodies fed by meltwater from alpine glaciers (e.g. Lake Vanda, Hendy, 2000[5]). The Wilson Piedmont Glacier was less extensive than at present from c. 3.1 14C ka BP onwards until c. 0.9 14C ka BP (c. 3.5-3.2 and 1.1-0.8 ka BP; (Hall and Denton, 2000[2])).

The past 2,000 years – Late Holocene warm period and recent rapid climate change

In contrast to the AP, the warmest conditions in the RS region during the Holocene did not occur during the mid Holocene but rather during the late Holocene, as evidenced by the presence of elephant seal hairs. The warmest period of the past 6,000 years occurred between c. 2.3 and 1.1 ka 14C BP (c. 2.6-2.3 and 1.2-0.9 ka BP) accompanied by the greatest decline in sea ice, as evidenced from an expansion of the elephant seal colonies (Hall et al., 2006[9]), and substantial abandonment of penguin sites (Emslie et al., 2007[10]). This period was followed by a period of enhanced evaporation, which lasted until 1 ka BP, when Lakes Fryxell, Vanda and Bonney evaporated to ice-free hypersaline ponds by c. 1.2-1 ka BP (Lyons et al., 1998[16]; Wagner et al., 2006[8]), and when Lake Wilson, a perennially ice-capped, deep (>100 m) lake further South (80°S) in southern Victoria Land, similarly evaporated to a brine lake (Webster et al., 1996[17]). After 1 ka BP, warmer and wetter conditions led to increasing water levels and primary production in the lakes (Lyons et al., 1998[16]; Wagner et al., 2006[8]). This has been attributed to higher summer temperatures or to an increase in the number of clear, calm and snowless midsummer days (Hendy, 2000[5]). During the last few centuries (< c. 0.2 14C ka BP, c. 0.4-0.1 ka BP) the Wilson Piedmont Glacier was more extensive than today in some areas until AD 1956 (Hall and Denton, 2002[7]). There is no sign in the McMurdo Dry Valleys of the pattern of glacier advances typical of the Northern Hemisphere Little Ice Age (Hall and Denton, 2002[7]).

Studies in the framework of the US Long Term Ecological Research program have revealed a rapid ecosystem response to local climate cooling in the McMurdo Dry Valleys during recent decades, as evidenced by a decline in lake primary production and declining numbers of soil invertebrates (Doran et al., 2002[18]).


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