@article{THESIS,
      recid = {2760},
      author = {Meadows, Caitlin Ana},
      title = {Community-Level Biotic Response to Increasing Climate  Variability During the Last 150 Years: Steady and Warming  Conditions on the Continental Shelf of the Pacific Arctic},
      publisher = {University of Chicago},
      school = {Ph.D.},
      address = {2020-12},
      number = {THESIS},
      pages = {223},
      abstract = {Ecosystem monitoring since 1980 has established that the  boundary between the Arctic and the Subarctic has shifted  northward on the Bering continental shelf between 1998 and  2001. However, such quantitative benthic data have been   collected consistently only since the 1980’s, whereas  additional long term data are available from natural  history collections (NHCs) since 1865 and from locally  accumulating dead-shell assemblages. By extracting and  integrating insights from these diverse sources, I address  the following questions: (1) Do dead-shell assemblages  capture the shifting Subarctic-Arctic boundary in the  Pacific Arctic ecosystem? (2) How long does biogenic carbon  persist on the Pacific Arctic continental shelf? (3) What  is history of bivalve family geographic distributions in  the N Bering and Chukchi Seas over the last 150 years? 

In  habitats where either Subarctic or Arctic conditions have  persisted over the last 40 years, bivalve death assemblages  agree closely with counterpart living communities in taxon  and guild composition and are not subject to significant  post-mortem bias. Significant live-dead discordance occurs  only in areas with documented changes in community  composition; there, dead assemblages are mixtures of shells  from pre- and post-transition communities. This spatial  pattern is robust in both numerical abundance- and  biomass-based measures of community composition. Live-dead  discordance can thus reliably differentiate between stable  and rapidly changing habitats in cold, high-latitude  settings, relevant to evaluating climate change.

Overall,  shells from Arctic death assemblages are young: all  specimens of Nuculana are < 1600 years old with a median  age of 50 years, and all Macoma shells are < 850 years old  with a median age of  about 30 years. These maximum shell  ages are an order of magnitude lower than encountered at  lower latitudes, while median shell ages are similar to  those at lower latitudes. The lowest median shell ages and  highest rates of shell loss are in the northern Bering Sea  and the southeastern Chukchi Sea, which are consistent  centers of high benthic oxygen demand and high seafloor  biomass. These results indicate that, within the Arctic,  shell preservation is more strongly correlated with benthic  biological activity than with the temperature and chemistry  of overlying water.

Using occurrence data for seven  families extracted from NHCs, long-stable bivalve  communities underwent a significant reorganization between  1940 and 1960. The biogeographic boundaries recognized from  NHC occurrence data do not differ significantly from those  based on quantitative biomonitoring data during the window  of 1970-2000 when both data types are available. These  findings indicate that the ecologic baseline inferred from  the first quantitative surveys in the 1970s captures a  recently completed (1960s) reorganization of the benthic  community, which coincided with the initial, 20th-century  onset of seasonal sea ice retreat.  

In addition to these  chapters the following supplementary documents are  included: a copy of “Estimating fossil biomass from  skeletal mass in marine invertebrates” published in Lethaia  (Appendix B_Meadows_Biomass_Lethaia.zip), complete datasets  of death assemblages (Appendix C_SWL14_FAMILY_Dead  Collected_Bivalve Taxa.zip), age dating calibrating models  (Appendix D_AAR_ALASKA_Bivalve_Meadows_Kidwell.zip), and  Arctic NHCs (Appendix J_ARCTIC_NHC_Bivalve  taxa_Meadows.zip). },
      url = {http://knowledge.uchicago.edu/record/2760},
      doi = {https://doi.org/10.6082/uchicago.2760},
}