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Woods Hole Oceanographic Institution

Kelton McMahon

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Projects
» Historical shifts in plankton communities

» Food web architecture in coral reefs

» Seascape connectivity of reef fish

» Ocean isoscapes

» Ocean-basin scale migrations of large pelagic fishes

» Bivalves as bioproxies for climate change

» Digestibility of Ice Algae and Phytoplankton

» Fundulus heteroclitus


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Enlarge image
A global isoscape of seawater δ18O (McMahon et al. in review OMBAR). ()


Developing ocean isoscapes for ecogeochemistry studies in the marine environment

Collaborators:
Dr. Simon R. Thorrold (WHOI), Dr. Li Ling Hamady (WHOI), Dr. Brittany Graham (NIWA), Dr. Seth Newsome (University of Wyoming), Dr. Paul Koch (UC Santa Cruz), Ms. Nora Hanson (University of St. Andrews)

The acquisition and allocation of resources is a fundamental requirement for all animals and significantly influences behavior, population dynamics, and ecosystem functioning. Stable isotope analysis (SIA) and other geochemical methods have been used extensively in food web studies and, more recently, to trace animal movements across habitats with distinctive isotopic signatures. However, while stable isotopes have been used in animal migration studies in terrestrial environments for several decades, the approach has received far less attention in marine systems. This lack of effort may be due, at least in part, to a failure to recognize the degree of geographic variation in isotope and element abundances across marine environments. In this project, we assemble global ocean isoscapes for key elements in marine ecogeochemistry including seawater hydrogen (δ2HSW), dissolved inorganic carbon (δ13CDIC), seawater radiocarbon (Δ14CSW), plankton carbon (δ13CPLK), plankton nitrogen (δ15NPLK), and seawater oxygen (δ18OSW). We also summarize distributions of those minor and trace elements consistently and accurately analyzed in the calcified tissues of marine fish and invertebrates and used as natural geochemical tags of natal origin. These maps reveal substantial spatial variability stable isotope values on regional and ocean-basin scales. We are continuing to expand the global isoscapes, incoporating new data and refining mapping techniques.  We are also moving towards the development of temporally explicit isoscapes. In addition, we hope to begin developing a process-based, coupled biogeochemical-physical ocean model to reconstruct baseline marine isoscapes for studies of top consumer movement and trophic ecology. Publications:

Graham BS, Koch PL, Newsome SD, McMahon KW, and Aurioles D (2009) Using isoscapes to trace the movements and foraging behavior of top predators in oceanic ecosystems. In Isoscapes: Understanding Movement, Pattern and Process on Earth Through Isotope Mapping (eds. J. West, G. J. Bowen, T. E. Dawson, K. P. Tu). pp. 299-318, Springer, New York

McMahon KW, Hamady L, Thorrold SR (2013) A review of ecogeochemistry approaches to estimating movements of marine animals. Limnology and Oceanography 58:697-714

McMahon KW, Hamady L, Thorrold SR (2013) Ocean ecogeochemistry – A review. Invited review for Oceanography and Marine Biology: An Annual Review
51:327-374


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