ABSTRACT: Holocene climate records in Northwest North America: new perspectives onunifying patterns of terrestrial and marine ecosystem change.

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As northwest North America experiences historically unprecedented rates of warming (>+1.0°C/decade since 1966, ACIA 2005), Holocene records of natural climate variability in the region are of increasing interest. New multiple-proxy records from ice and lake sediments provide a first glimpse of Northeast Pacific watercycle/ oxygen-isotope dynamics during the Holocene and lead towards a unifying conceptual model of North Pacific atmospheric circulation. In this presentation, we explore linkages between Holocene climate patterns, Gulf of Alaska marine ecosystem and landscape change in Alaska and Yukon Territory. Oxygen isotope ratios from Jellybean Lake carbonate sediments and ice cores from Mount Logan (5959 m a.s.l.), both located in the southwest Yukon Territory, record modern modes of climate variability such as the North Pacific Index (NPI) and Pacific Decadal Oscillation (PDO) and extend regional climate records back to the early Holocene (Osterberg et al., 2006, Anderson et al., 2005). Comparisons with instrumental climate data and computer models indicate that d18O in precipitation is controlled primarily by vapor source and transport rather than reflecting changes in temperature of condensation (Anderson et al, 2005; Fisher et al., 2004). Both Jellybean Lake and Mount Logan d18O records show prominent negative shifts ~1840 A.D. and ~1200 yr BP and suggest that decadal to multi-decadal atmospheric circulation variations are characteristic of North Pacific Holocene climate variability. There is general agreement that North Pacific climate is dynamically related to tropical sea surface anomalies and the El Nino-Southern Oscillation (e.g., McPhaden et al., 2006; Moore et al., 2003; Niebauer, 1988). The interaction between topographically complex landscapes and dominant storm tracks determines modern climate patterns in Alaska and the Yukon. Circulation around the semi-permanent Aleutian Low drives storms into the ~3000-m high St. Elias and Coast Mountain barrier resulting in high precipitation on the coastal side of the mountains (~6000 mm/yr) and a strong rain shadow in the low-lying interior valleys (<260 mm/yr). If Jellybean Lake and Mount Logan document past changes in the intensity and position of storm tracks during the past, do their records correspond with past climate patterns on the landscape? This question was explored using sediments from hydrologically-closed Marcella Lake, located in the rain shadow of the St. Elias massif and CoastMountains. Marcella Lake has been sensitive to changes in moisture balance (precipitation-evaporation) throughout the Holocene. Changes in carbonate d18O reflect changes in lake evaporation and indicate that wetter-than-modernconditions between ~3000 and 1200 yr BP were followed by increasingly arid conditions that persist to the present (Anderson et al., 2006). Comparison between Marcella Lake evaporation and regional neoglacial activity suggests two late Holocene climate patterns, 1) simultaneous wet conditions at high coastal-mountain elevations and low, leeward elevations or, 2) wet conditions in the mountains and dry conditions at low, leeward elevations in the interior. These climate patterns correspond well with circulation documented by Jellybean Lake and Mount Logan. When the Aleutian Low was weaker and/or westward, moisture was more effectively delivered into NWSE trending interior valleys, and increased low-elevation effective moisture. When the Aleutian Low was intensified and/or eastward, stronger and/or more persistent down-slope, leeward winds reduced low-elevation effective moisture in the rain shadow.Modern modes of North Pacific climate variability are closely related to sea-surface temperatures, fresh-water run-off and marine ecosystem productivity. Changes in Gulf of Alaska primary and secondary ocean productivity indicate that climate forcing has direct impacts on lower trophic levels, which subsequently affects salmon production, probably through food availability (e.g., Mundy, 2005). Past salmon abundances have been reconstructed from d15N of organic sediments in nursery lakes. Marine-derived, 15N-enriched nutrients are preserved when Salmon return to nursery lakes to spawn and die. Records of ocean productivity, which generally correlate with salmon abundance, may provide a mechanistic linkage between climate change and salmon populations (Addison et al., 2006). Prominent shifts from low to high abundance recorded in Karluk Lake, Alaska correspond to an eastward and/or intensified Aleutian Low (Anderson et al., 2005; Finney et al., 2002) and raise the possibility that Pacific salmon abundance variations throughout the Holocene can be attributed to multidecadal atmospheric circulation variations in the Northeast Pacific. The concept of multi-decadal atmospheric circulation variations has unified a number of prominent Holocene shifts and trends, but numerous discrepancies and questions will drive the next generation of investigations. For instance, climate-salmon relations during the Holocene do not always follow patterns observed in the 20th century (Finney and Addison, 2006) and there are intriguing periods when the Mount Logan and Jellybeanrecords diverge. It has been observed that the winters of 1999-2002 were characterized by circulation that bears little resemblance to weak/strong (+/-) PDO patterns (Bond et al., 2003). Furthermore, there is considerable uncertainty regarding the current mode state of the North Pacific and if the PDO sufficiently captures all significant natural variations (Overland and Bond, 2006; Bartlein, 2006;). For future studies it will be necessary to consider multiple models of North Pacific climate variability in addition to regional feedbacks which characterize the region (Edwards et al., 2006), especially at times when spatial patterns diverge from expected fixed periods or cycles.

Bibliography of Canadian Geomorphology