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Principal Investigators: Karl Kreutz, Hal Borns, Douglas Introne

The primary goal of this research is to develop a detailed calibration of the Mytilus edulis isotope paleothermometer using organisms from Maine and Greenland aquacultured under controlled conditions. The secondary goal is to apply the calibrated isotope paleothermometer to fossil M. edulis shells collected in coastal Maine, and provide quantitative estimates of deglacial oceanographic conditions to test hypotheses that link glacier dynamics and climate variability ca. 15,000 Ð 13, 000 ¹⁴C yrs. BP. Despite the nearly 50 year history of using the oxygen isotopic composition of carbonate bivalve skeletons (δ¹⁸O_c) to reconstruct environmental conditions, a fundamental problem remains that limits quantitative paleoceanographic interpretations. Namely, several factors in addition to water temperature, including the isotopic composition of water (δ¹⁸O_w) and its relation to salinity, complicate the climate signal recorded in d¹⁸O_c. Without detailed, empirical calibrations between δ¹⁸O_c, δ¹⁸O_w/salinity, and water temperature under controlled conditions, quantitative reconstructions of past oceanographic and climate conditions are limited. This problem is particularly relevant to coastal and ice marginal locations, where variable δ¹⁸O_w/salinity conditions are encountered and affect M. edulis δ¹⁸O_c independently of temperature. The significance of the calibrated M. edulis isotope paleothermometer is that other investigators can apply it to location- and time-specific paleoclimate reconstructions. Further, the methods developed in this project can serve as a template for the isotope calibration of other carbonate-secreting organisms.

The proposed methodology builds on our successful pilot study experiment, where M. edulis larvae from coastal Maine were aquacultured and isotope measurements made on larvae carbonate. We now seek to expand our efforts temporally and geographically, with the following research objectives over the two-year project period:

• Design and develop aquaculture-based techniques for monitoring M. edulis growth in controlled water temperature, salinity, and δ¹⁸O_w conditions;
• Determine empirical relationships between shell δ¹⁸O_c, water temperature, and salinity/δ¹⁸O_w for M. edulis collected in Maine;
• Quantify any vital effects occurring under different environmental and/or age conditions that affect shell isotopic composition;
• Culture M. edulis collected from Greenland, and investigate any location-specific effects on isotopic composition;
• Develop age/location-specific transfer functions for temperate and polar M. edulis, and apply the calibrated paleotemperature equation to M. edulis shells collected from emerged ¹⁴C-dated glaciomarine sediments in coastal Maine.

Broader impacts of the proposed research include the following: 1) Techniques and ideas developed in the project will be used in several interdisciplinary courses at both the undergraduate and graduate levels (GES 527 Isotope Geology; GES 441 Glacial Geology; and SMS 309-409 Shellfish Aquaculture), and contribute to student research training in the UMaine Marine Culture Laboratory and Stable Isotope Laboratory; 2) A graduate student and at least one undergraduate student will participate in all aspects of the research, and at least one MS thesis and several peer reviewed publications will be produced; 3) Significant improvements to aquaculture infrastructure at UMaine will occur, thereby providing opportunities for future expansion of shellfish proxy calibration and other related research; 4) International collaboration with Danish colleagues will facilitate research on modern Greenland marine fauna in this project and future efforts with applications to other circum-North Atlantic late glacial stratigraphies; 5) Fundamental contributions to shellfish isotope proxy interpretation are expected, and will benefit researchers in several interdisciplinary fields including paleoclimatology, paleoceanography, and marine biology; and 6) Public outreach will include a project website, and incorporation of data and ideas in the developing Ice Age Trail, an interactive roadside geotour of Downeast coastal Maine focusing on the effects of the Laurentide Ice Sheet on local geomorphology, paleoclimate, and paleoecology.