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Generating Past ENSO and PDO Indices at Seasonal Timescales from Ultrahigh-Resolution Marine Sediment Records in the Gulf of Alaska: Jason A. Addison


Project Title: Generating Past ENSO and PDO Indices at Seasonal Timescales from Ultrahigh-Resolution Marine Sediment Records in the Gulf of Alaska
Mendenhall Fellow: Jason A. Addison, jaddison@usgs.gov
Start Date: October 1, 2010
Education: Ph.D. (Geology), University of Alaska Fairbanks, 2009
Research Advisors: John Barron, (650) 329-4971, jbarron@usgs.gov; Lesleigh Anderson, (303) 236-1296), land@usgs.gov; Bruce Finney, (208) 382-4318, finney@isu.edu

Project Description: High-latitude regions of the Northern Hemisphere are currently experiencing rapid environmental change thought to be a result of combined forcing by natural and anthropogenic processes. In many regions of Alaska, these observed changes include the rapid retreat of formerly advancing glaciers in both alpine and coastal settings, thawing permafrost, the release of methane and other greenhouse gases stored in frozen reservoirs, and widespread shifts in terrestrial and marine biogeographic distributions. Many of these observations are unprecedented in recent history and their impacts are largely unknown. This uncertainty stems from the relatively short period of instrument observations that span the last century. High-quality paleoclimate datasets are therefore essential for reconstructing earlier climate histories, yet the spatial coverage of such records remains sparse. This scarcity complicates climate modeling efforts that are necessary for better anticipating future climate impacts for society.

Northern Hemisphere correlation maps between winter precipitation and (a) ENSO or (b) PDO climate regimes   The Gulf of Alaska is a dynamic region located in the transition zone between the continental Arctic and temperate southern latitudes of North America. It dominates the subarctic northeast Pacific Ocean, an important component of Northern Hemisphere climate patterns with atmospheric teleconnections reaching as far east as the U.S. Atlantic Coast, and as far south as the Sonora Desert in northern Mexico (fig. 1) (Wallace and Gutzler, 1981). Modern observations indicate the Gulf of Alaska is sensitive to both annual and decadal climate variability.  Precipitation, sea surface temperatures, and fluvial discharge all show strong correlations to both the interannual El Niño–Southern Oscillation (ENSO) (fig. 1a) index (Whitney and Freeland, 1999), and the Pacific Decadal Oscillation (PDO) (fig. 1b) index (Mantua and others, 1997). There is also strong evidence that both the ENSO and PDO regimes strongly regulate the Gulf of Alaska marine ecosystem at multiple trophic levels. Such a link has been well described for PDO climate cycles driving historic and ancient Pacific sockeye salmon abundances (Finney and others, 2000).  Clearly, understanding such high-frequency climate regimes in the context of high-latitude change is critical.

Newly acquired marine sediment cores from the Gulf of Alaska present a rare opportunity to take advantage of high sedimentation rates to examine past climate at seasonal time scales. With the objective of better understanding future climate impacts in this sensitive high-latitude setting, state-of-the-art X-ray fluorescence (XRF) core-scanning technology (Richter and others, 2006) will be used with multi-proxy biogeochemical analyses of annual layers (varve couplets) from several marine sediment cores located in southeast Alaskan nearshore fjords. These sites are exceptional archives of marine productivity and terrestrial precipitation that are controlled by regional atmospheric and ocean conditions at seasonal, annual, and decadal timescales. The objective of this work is to develop a record of annual climate variability from the Gulf of Alaska region and then use this record to quantify ENSO and PDO activity during the last 5,000 years. These data will be integrated with other Northern Hemisphere paleoclimate datasets to understand this uniquely high-latitude ENSO and PDO climate record. The predictive capabilities inherent in these paleoENSO and paleoPDO indices will bring the scale of past climate change into the same timeframe as that of modern human observations, thus allowing natural climate cycles from the past to be distinguished from more recent climate trends that may have been affected by human-induced environmental perturbations.

Key research questions include:

    • Can proxies of ENSO variability be resolved in coastal Alaskan sediment records? If so, what is the strength and periodicity of this past ENSO variability in the Gulf of Alaska?
    • Have the ENSO and PDO indices maintained constant configurations between sea surface temperature, precipitation, and ecosystem variability over timescales exceeding the span of human observations (for example, beyond the last 100 years)?
    • Did ENSO and PDO dynamics undergo shifts during the late Holocene Neoglacial cooling, the Medieval Warm Period, the Little Ice Age, and 20th century warming?
    • How do high-latitude ENSO and PDO records compare with those from lower latitudes?

Selected References

Finney, B.P., Gregory-Eaves, I., Sweetman, J., Douglas, M.S.V., and Smol, J.P., 2000, Impacts of climatic change and fishing on Pacific salmon abundance over the past 300 years: Science, v. 290, no. 5492, p. 795–799.

Mantua, N.J., Hare, S.R., Zhang, Y., Wallace,J.M., and Francis, R.C., 1997, A Pacific interdecadal climate oscillation with impacts on salmon production, Bulletin of the American Meteorological Society, 78(6), 1069–1079.

Richter, T.O., van der Gaast, S., Koster, B., Vaars, A., Giele, R. de Stigte, H.C., De Haas, H., and van Weering, T.C.E., 2006, The Avaatech XRF Core Scanne Technical description and applications to NE Atlantic sediments, in Rothwell, R.G., ed., New techniques in sediment core analysis: London, Geological Society of London Special Publication 267, p. 39–50.

Wallace, J.M., and Gutzler, D.S., 1981, Teleconnections in the geopotenital height field during the Northern Hemisphere winter: Monthly Weather Review, v. 109, no. 4, p. 784–812.

Whitney, F.A., and Freeland, H.J., 1999, Variability in upper-ocean water properties in the NE Pacific Ocean: Deep-Sea Research, Part II, Topical Studies in Oceanography,v. 46, no. 11–12,p. 2351–2370.

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