Characterizing Arctic Ocean Sea Ice Environments across the Distributed Biological Observatory: From Melt Ponds to Phytoplankton Community Structure

• Main Author: Young, Luisa Malua Natasha Crystale
• Format: Dissertation
• Language: English
• Published: ProQuest Dissertations & Theses 01-01-2022
• Subjects: Geographic information science; Geography; Remote sensing
• ISBN: 9798438722021

The Arctic is warming twice the rate of the global average. A key indicator of that warming has been the unprecedented loss of sea ice which has triggered a cascading array of shifts in terrestrial and marine ecosystems. The effects transcend multiple scales, with implications for global climate and ocean circulation, ecosystem structure (i.e. species biodiversity) and human ecological systems (i.e. native livelihoods, fishing industries). While satellite measurements and long-term monitoring programs provide insight into these changes, there is still limited understanding of how and where these changes will occur and whether Arctic sea ice has already crossed a threshold from which it is unable to recover. Despite the mixed scientific consensus of sea ice reaching such a point, Arctic sea ice has been on a drastic decline over past 40 years with regional and global consequences that are not fully understood yet. This multi-faceted study seeks to characterize how the Arctic seascape has changed over the last two decades through change detection of sea ice break-up and freeze-up timing, linkages to melt pond variability and the impacts to lower trophic level phytoplankton community assemblages. The studies in this dissertation focus upon the Pacific Arctic region and the Distributed Biological Observatory (DBO) sites therein. The sites consist of eight transects situated across highly productive and biodiverse areas in the Bering, Chukchi, and Beaufort Seas. In order to gain an understanding of the Pacific Arctic sea ice-oceanic regime in a changing climate this research combines long-term remotely sensed observations and field collected samples across the DBO sites. In particular, this dissertation addresses three goals. Goal 1 is to identify abrupt breakpoints and regime shifts in the timing of break-up and freeze-up of sea ice in the DBO sites. Results show that the DBO sites have experienced at least one breakpoint over the last two decades with DBO 3 and 4 exhibiting abrupt regime shifts in the timing of sea ice retreat and formation. Goal 2 is to develop a melt pond product using a novel multi-temporal, multiple endmember spectral unmixing analysis (MESMA) approach of Moderate Resolution Imaging Spectroradiometer (MODIS) 500 m spectral reflectance data to quantify trends in melt pond intensity and duration across the Pacific Arctic. Results indicate that melt pond duration and intensity (i.e., seasonal magnitude) have increased across the DBO stations over the last 21-years of the satellite record. Goal 3 is to assess phytoplankton community structure (including abundance and biovolumes) through the water column at each DBO site to determine their distribution and key environmental ranges. Results show a clustering of a diatom dominated group in DBO 3 located in the southern Chukchi Sea and a smaller-sized group consisting primarily of dinoflagellates and other nanoflagellates concentrated in DBO 1, south of St. Lawrence Island in the Bering Sea. The diatom group were strongly associated with chlorophyll-a, highlighting a bloom forming community, and salinity whereas the dinoflagellate group had a weak association to temperature, depth, sea ice break-up, and silicate. This dissertation provides a long-term assessment of change across the sea ice-oceanic environment in the Pacific Arctic, evaluates previously unknown trends of melt ponding and abrupt breakpoints across the DBO sites and assesses phytoplankton community structure for an anomalously warm year in the region. These finding has vast implications for understanding Arctic change and how these multiple systems may respond to further climate warming.