Gulf of Alaska | Climate and Oceanography MASTER’S POSTER PRESENTATION Assessing humpback whales’ role in the carbon and nutrient cycles of southeast Alaska Presenter: Dana Bloch , dbloch@alaska.edu, UAF-CFOS
Tyler Hennon , tdhennon@alaska.edu, University of Alaska Fairbanks Heidi Pearson , hcpearson@alaska.edu, Univeristy of Alaska Southeast Andy Szabo , andyszabo@gmail.com
Continued anthropogenic warming of surface oceans will lead to increased thermal stratification and nutrient limitation, resulting in an expected decline in the rate of photosynthetic carbon production. Whales may play an important role in nutrient and carbon cycling through a process called the whale pump, whereby whales feed at depth and release fecal matter rich in limiting nutrients to the euphotic zone, stimulating local primary production. This project examines the whale pump in Southeast Alaska (SEAK), foraging grounds for over 1500 humpback whales ( Megaptera novaeangliae ). Oceanographic data in SEAK are sparse and irregular in time and space, but consistent measurements will help to contextualize the potential significance of the whale pump. We characterized local environmental parameters with systematic vertical profiles using an oceanographic probe (CTD) (n = 685), measuring temperature, salinity, and fluorescence, alongside strategically located water samples (n = 464) for nutrient analysis. Additionally, we are partnering with the Alaska Troller’s Association who deploy CTDs monthly at select stations throughout the year. Whale fecal samples (n = 19) were collected opportunistically. Both water and fecal samples were analyzed for nitrate, nitrite, ammonium, and phosphate concentrations. Preliminary results show shallow summertime surface mixed layers (1-10 m), with higher nutrient concentrations at depth than in the surface ocean. Fecal nutrient concentrations appear much higher than nearby ambient waters. The next step will be to perform an incubation experiment to help assess the effect of fecal matter on phytoplankton. Future work will also include an order of magnitude calculation of potential primary productivity stimulated by humpback fecal matter. This initial oceanographic characterization marks the start of an effort to map patterns in SEAK and to better track changes over time. Ultimately, this work will improve our understanding of humpback whale aggregations and their impact on regional carbon and nutrient cycling, which may have increased importance as ocean warming intensifies stratification and coastal ecosystems undergo shifts in nutrient concentrations and ratios.
Alaska Marine Science Symposium 2023 102
Made with FlippingBook flipbook maker