Research Projects
Here are a few of the research projects active in our lab:
1. The Global Anthropogenic Lead Experiment
Almost all of the lead in the ocean derives from human emissions from high temperature industrial activities (smelting, coal combustion, incineration, etc.) and leaded gasoline utilization. Most of this lead was emitted in the past 100 years with peak U.S. emissions in the 1970's. A large fraction of this Pb is attached to fine particles and moves with the global atmospheric circulation before being deposited in remote regions.
We have been studying this "global geophysical experiment" by following the evolution of Pb in ice cores and in the ocean. We have measured Pb in surface and deep seawater samples for the past 20 years, and we can estimate Pb for the preceding century using Pb in annually-banded corals. The emitted 206/207 and 208/207 Pb isotope ratios have evolved during the past 120 years so that it is sometimes possible to "date" the Pb in an environmental sample by measuring the isotope ratios.
2. Iron in the Ocean: physical form and possible link to marine nitrogen fixation
Iron is extremely insoluble in the ocean and its concentration is so low in parts of the ocean (the "high nutrient low chlorophyll" regions) that it is insufficient to support the growth of marine phytoplankton. Iron is also particularly essential to organisms that fix nitrogen using the nitrogenase enzyme. Yet despite this important role in regulating ocean biogeochemistry, there is very little data on iron in the ocean because of the extreme difficulties associated with clean sample collection on rusty ships and its analysis at low concentration levels. We have developed small-volume (1.3 ml) methods for the analysis of iron in seawater using collision-cell plasma mass spectrometry. In addition, we have developed methods for the distinction of colloidal (0.02-0.4 µm) iron from truly soluble iron (<0.02 µm). We have been working with marine biologists and atmospheric dust scientists to study the relationship between dust, iron in the ocean, and nitrogen fixation as part of a five-year NSF-funded "Biocomplexity" program.
3. What is the Link Between Deep Ocean Circulation and Abrupt Climate Change?
Studies of ice cores from Greenland show that in the period between 30,000 to 60,000 years ago, there were a succession of 17 abrupt warmings after severe glaciations followed by an almost equally abrupt shift back to glacial conditions. Many scientists think that these shifts are due to instabilities in the deep ocean circulation. But there is very little evidence showing a link between ocean circulation and these events. In order to bridge this gap, we are analyzing fossil deep sea benthic foraminifera from a 53-meter sediment core on the Bermuda Rise to watch the changes between high percentages of North Atlantic Deep Water (low Cd) and high percentages of Southern Ocean Deep Water (high Cd).
4. What mechanisms control isotope variability of iron and zinc isotopes in the marine environment?
The arrival of multi-collector plasma mass spectrometry has made it possible to analyze transition metal isotopes. Most workers in this field are focusing on high-metal concentration samples such as rocks, ores, and ferromanganese crusts and nodules; they have found evidence for significant iron and zinc isotope fractionations in time and space. Because these elements occur at very low levels in the ocean, and because sample contamination is a serious problem, few people are investigating these isotopes in seawater and other low-level marine samples. By analogy to the utility of carbon and nitrogen isotope systems, we propose that the iron and zinc isotope systems will help us better understand the biogeochemistry of these biologically-essential trace elements: after the basic ground rules are established. Graduate students Bridget Bergquist and Seth John are doing this ground-breaking work in our laboratory.
5. CMORE: Center for Microbial Oceanography: Research and Education
C-MORE is a recently established (August 2006) NSF-sponsored Science and Technology Center designed to facilitate a more comprehensive understanding of the diverse assemblages of microorganisms in the sea, ranging from the genetic basis of marine microbial biogeochemistry including the metabolic regulation and environmental controls of gene expression, to the processes that underpin the fluxes of carbon, related bioelements and energy in the marine environment. Stated holistically, C-MORE’s primary mission is: Linking Genomes to Biomes. Partner Institutions involved in this project, in addition to MIT, are the University of Hawaii, Woods Hole Oceanographic Institution, Monterey Bay Aquarium Research Institute, UC Santa Cruz, and University of Oregon. MIT PIs include Penny Chisholm and Ed DeLong. Our role in this project is in linking microbial ecology and genetics with the upper ocean geochemistry of iron, an essential trace micronutrient.
This page was last revised on Oct. 26, 2006