Climate variability in glacial fjords

A poster summarizing our long-term study in Port Valdez was presented at the Western Society of Naturalists in San Diego.  The data presented were the abundance and biomass of fauna found in the sediments of the deep basin of Port Valdez.  Port Valdez has two sills (underwater terminal moraines at the mouth of the fjord) and a deep basin (> 240 m). The general shape of the basin of the fjord is like a bathtub resulting in limited exchange of the deep water with surface layers. Thus, the fauna of the deep basin are thought to be less affected by short-term fluctuations at the surface and more responsive to annual cycles.

I found two trends in the database representing large-scale variations.  The first was a response to the Great Alaska Earthquake in 1964 and the second was an association with the Pacific Decadal Oscillation (PDO). The PDO is a measure of sea surface temperatures in the North Pacific Ocean and has been shown to be associated with large-scale variations in biological characteristics of the North Pacific including survival and recruitment of fish stocks. Glacial fjords may be particulary sensitive to climatic variability through variations in the melting rates of glaciers.  Warmer oceans = more rain and higher temps = faster melting = increased runoff flow into fjords.

 Although the deep basins of fjords are somewhat isolated from short-term changes in surface waters, many invertebrate larvae spend some time in surface waters so the deep subtidal fauna community composition will be influenced by environmental change through larval recruitment.  For example, field studies have shown that survival of bivalve larvae is influenced by water temperature.  Thus, the pathway exists for long-term climatic variability to influence benthic communities through pathways other than food web variations. 

In my work, I found a positive association with the overall abundance of infaunal animals in the deep basin of Port Valdez, Alaska.  This plot shows the trends in average abundance of stations in the deep basin and the average PDO index value for each year.  The tight association between the two values after 1987 is remarkable.  The lack of trend prior to 1987 is also interesting and appears to be related to a recovery process from the 1964 earthquake (a topic to follow).

 I haven't yet had the chance to explore the data to understand how the communities respond to the PDO but the data indicate a pretty strong relationship.  Our next step is to mine the data to find animals whose abundances are positively and negatively associated with the trends in the PDO.