Freshening of the Alaska Coastal Current Recorded By Coralline Algal Ba/Ca Ratios

Arctic Ocean freshening can exert a controlling influence on global climate, triggering strong feedbacks on ocean-atmospheric processes and affecting the global cycling of the world's oceans. Glacier-fed ocean currents such as the Alaska Coastal Current are important sources of freshwater for the Bering Sea shelf, and may also influence the Arctic Ocean freshwater budget. Instrumental data indicate a multiyear freshening episode of the Alaska Coastal Current in the early 21st century. It is uncertain whether this freshening is part of natural multidecadal climate variability or a unique feature of anthropogenically induced warming. In order to answer this, a better understanding of past variations in the Alaska Coastal Current is needed. However, continuous long-term high-resolution observations of the Alaska Coastal Current have only been available for the last 2 decades. In this study, specimens of the long-lived crustose coralline alga Clathromorphum nereostratum were collected within the pathway of the Alaska Coastal Current and utilized as archives of past temperature and salinity. Results indicate that coralline algal Mg/Ca ratios provide a 60 year record of sea surface temperatures and track changes of the Pacific Decadal Oscillation, a pattern of decadal-to-multidecadal ocean-atmosphere climate variability centered over the North Pacific. Algal Ba/Ca ratios (used as indicators of coastal freshwater runoff) are inversely correlated to instrumentally measured Alaska Coastal Current salinity and record the period of freshening from 2001 to 2006. Similar multiyear freshening events are not evident in the earlier portion of the 60 year Ba/Ca record. This suggests that the 21st century freshening of the Alaska Coastal Current is a unique feature related to increasing glacial melt and precipitation on mainland Alaska.

Ice Layers as an Indicator of Summer Warmth and Atmospheric Blocking in Alaska

Samples were collected from a snow pit and shallow urn core near Kahiltna Pass (2970 m a.s.l.), Denali National Park, Alaska, USA, in May 2008. The record spans autumn 2003 to spring 2008 and reveals clusters of ice layers interpreted as summertime intervals of above-freezing temperatures. High correlation coefficients (0.75-1.00) between annual ice-layer thickness and regional summertime station temperatures for 4 years (n=4) indicate ice-layer thickness is a good proxy for mean and extreme summertime temperatures across Alaska, at least over the short period of record. A Rex-block (aka high-over-low) pattern, a downstream trough over Hudson Bay, Canada, and an upstream trough over eastern Siberia occurred during the three melting events that lasted at least 2 weeks. About half of all shorter melting events were associated with a cut-off low traversing the Gulf of Alaska. We hypothesize that a surface-to-bedrock core extracted from this location would provide a high-quality record of summer temperature and atmospheric blocking variability for the last several hundred years.

Cladorhiza corona sp. nov. (Porifera : Demospongiae : Cladorhizidae) from the Aleutian Islands (Alaska)

A new species of Cladorhizidac, front the Aleutian Islands is described and compared with all known species of Cladorhizza worldwide. Cladorhiza corona sp. now has a unique growth form with two planes of differently shaped appendages. Appendages are Inserted directly at the stalk; a spherical or conical body at the stalk is lacking. It is the only species reported where different spicule types occur in three morphologically different areas of the sponge. The spiculation of the basal plate is characterized by the occurrence of short, thick anisoxcas and the lack of anisochelae. Anisochelac arc found in the stalk and the basal appendages only. Flattened sigmancistras and (sub-)tylostyles are restricted to the crown. The arrangement of spicules is different in the basal plate, the stalk with the basal appendages, and in the distal append ages. The dimensions and combination of spicule types separate C. corona sp. nov. from all known members of the genus.

Twentieth Century Delta δC Variability in Surface Water Dissolved Inorganic Carbon Recorded by Coralline Algae in the Northern North Pacific Ocean and the Bering Sea

The oxygen isotopic composition and Mg/Ca ratios in the skeletons of long-lived coralline algae record ambient seawater temperature over time. Similarly, the carbon isotopic composition in the skeletons record delta(13)C values of ambient seawater dissolved inorganic carbon. Here, we measured delta(13)C in the coralline alga Clathromorphum nereostratum to test the feasibility of reconstructing the intrusion of anthropogenic CO(2) into the northern North Pacific Ocean and Bering Sea. The delta(13)C was measured in the high Mgcalcite skeleton of three C. nereostratum specimens from two islands 500 km apart in the Aleutian archipelago. In the records spanning 1887 to 2003, the average decadal rate of decline in delta(13)C values increased from 0.03% yr(-1) in the 1960s to 0.095% yr(-1) in the 1990s, which was higher than expected due to solely the delta(13)C-Suess effect. Deeper water in this region exhibits higher concentrations of CO(2) and low delta(13)C values. Transport of deeper water into surface water (i.e., upwelling) increases when the Aleutian Low is intensified. We hypothesized that the acceleration of the delta(13)C decline may result from increased upwelling from the 1960s to 1990s, which in turn was driven by increased intensity of the Aleutian Low. Detrended delta(13)C records also varied on 4-7 year and bidecadal timescales supporting an atmospheric teleconnection of tropical climate patterns to the northern North Pacific Ocean and Bering Sea manifested as changes in upwelling.

Ice Core Paleovolcanic Records from the St. Elias Mountains, Yukon, Canada

We previously reported a record of regionally significant volcanic eruptions in the North Pacific using an ice core from Eclipse Icefield (St. Elias Mountains, Yukon, Canada). The acquisition of two new ice cores from Eclipse Icefield, along with the previously available Eclipse Icefield and Mount Logan Northwest Col ice cores, allows us to extend our record of North Pacific volcanism to 550 years before present using a suite of four ice cores spanning an elevation range of 3 - 5 km. Comparison of volcanic sulfate flux records demonstrates that the results are highly reproducible, especially for the largest eruptions such as Katmai ( A. D. 1912). Correlation of volcanic sulfate signals with historically documented eruptions indicates that at least one-third of the eruptions recorded in St. Elias ice cores are from Alaskan and Kamchatkan volcanoes. Although there are several moderately large ( volcanic explosivity index (VEI) >= 4) eruptions recorded in only one core from Eclipse Icefield, the use of multiple cores provides signals in at least one core from all known VEI >= 4 eruptions in Alaska and Kamchatka since A. D. 1829. Tephrochronological evidence from the Eclipse ice cores documents eruptions in Alaska (Westdahl, Redoubt, Trident, and Katmai), Kamchatka (Avachinsky, Kliuchevoskoi, and Ksudach), and Iceland (Hekla). Several unidentified tephra-bearing horizons, with available geochemical evidence suggesting Alaskan and Kamchatkan sources, were also found. We present a reconstruction of annual volcanic sulfate loading for the North Pacific troposphere based on our ice core data, and we provide a detailed assessment of the atmospheric and climatic effects of the Katmai eruption.