Aquaculture-based calibration of the M. edulis isotope paleothermometer

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 13, 000 14C yrs. BP. Despite the nearly 50 year history of using the oxygen isotopic composition of carbonate bivalve skeletons (δ18Oc) 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 (δ18Ow) and its relation to salinity, complicate the climate signal recorded in d18Oc. Without detailed, empirical calibrations between δ18Oc, δ18Ow/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 δ18Ow/salinity conditions are encountered and affect M. edulis δ18Oc 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:

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.

geotour of Downeast coastal Maine focusing on the effects of the Laurentide Ice Sheet on local geomorphology, paleoclimate, and paleoecology.