Collaborative research: reconstructing bottom water temperatures from bivalves on the continental shelf: holocene history as a window to the future in the mid- atlantic

This National Science Foundation Project Grant under the Geosciences program (CFDA 47.050) totaling $103,519 will support collaborative research by the Woods Hole Oceanographic Institution from August 2022 to July 2025 to reconstruct bottom water temperatures on the Middle Atlantic continental shelf over the past 5,000 years using living and fossil shells of Atlantic surfclams and ocean quahogs. The grant aims to develop spatial-temporal reconstructions of bottom water temperatures to further understanding of past climate change in the region and its impacts on the two clam species' distributions. Specifically, the researchers will analyze isotopes in the clam shells to indicate the temperatures experienced hundreds to thousands of years ago and seasonally. They will determine the historical frequency and rapidity of major climate changes and corresponding range shifts, as well as potential climate drivers. The reconstructed records will inform retrospective models and projections of future range distributions under continued warming. The grant also includes educational outreach and training of undergraduate and graduate students.

Abstract

Reconstructing bottom water temperatures from bivalves on the continental shelf: holocene history as a window to the future in the mid-atlantic the ocean waters of the middle atlantic continental shelf off the east coast of the united states are warming rapidly. These continental shelf waters have a unique feature, the cold pool, that is formed when summer warming of surface waters traps cold winter water along the bottom. The cold pool is extensive but the area IT covers is expected to shrink as shelf waters warm. The cold pool is home to two bottom dwelling clam species, ocean quahogs and atlantic surfclams. These animals, especially ocean quahogs, are long lived. Records of growth and the temperature the clams experienced are preserved in their shells, similar to tree rings. The shells of live and fossil clams from the cold pool will be used to estimate bottom water temperature over the past ~5000 years. The bottom temperatures will be linked to past climate periods and known climate variability that influence the middle atlantic. Understanding cold pool changes is important for studying past climate change and projecting future changes for the middle atlantic region. The bottom water temperatures from the clam shells will show how clam distributions might change in response to climate warming. Changes in distribution are important because of possible economic impacts on the clam fishery. Training undergraduate and graduate students will be part of this project and will foster linkages between oceanography and paleoclimate science. Educational outreach programs for k-8 students and a science-related art initiative through the synergy project organized by art league RI will highlight the novel approach of asking clams to reveal changes in ocean bottom water temperature. The history of climate change on the middle atlantic continental shelf is recorded by the shells of two long-lived bivalves, the atlantic surfclam, spisula solidissima, and the ocean quahog, arctica islandica. Shell is deposited in layers as these clams grow. Analysis of the ratios of carbon (C12/C14) and oxygen (O16/O18) isotopes along the growth axes of the shell indicates the temperatures that were encountered by the growing clam hundreds to thousands of years ago, and also how this varied seasonally. The accumulation of fossil shells is termed a death assemblage. The temperature time series obtained from the living and fossil shells will be used to develop spatial-temporal reconstructions of bottom water temperatures on the middle atlantic shelf for the past ~5000 years. A cold pool of water forms each summer when stratification traps cold winter water along the shelf bottom below a layer of warmer water. Particular attention will be paid to variability in this cold pool. Understanding the history of climate change on the continental shelf will provide important information on past climatic changes in this region, the impact of these changes on ongoing range shifts of the two clam species, and allow projection of future range distributions. Analyses of the reconstructed bottom water temperatures will determine the historical frequency and, where possible, rapidity of major climatic changes and corresponding range shifts since the beginning of the neoglacial period. Potential climate drivers associated with the range changes will be determined from the reconstructed bottom-water temperatures and compared with other north atlantic reconstructions. The influence of bottom water temperature changes on the timing of clam mortality events will be assessed. The reconstructed bottom water temperature records will extend inputs for retrospective models and be related to changing species distributions (from collection location records) in the middle atlantic region. In turn these reconstructions provide the basis for forward projections with implications for continued warming on ecological processes and fishery production. This effort brings together scientists with a broad range of expertise, and notably includes both young investigators as lead investigators, and students at both the graduate and undergraduate level. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the foundation's intellectual merit and broader impacts review criteria.