The PAOC chemical oceanography group of Prof. Ed Boyle focuses on natural and anthropogenic metals in the ocean. It is a unique research lab at the forefront of its field.
Boyle’s research group works on trace metals and trace metal isotope ratios in the oceans, estuaries, rivers, and ice cores. Trace metals are used as probes of the modern ocean (e.g., Pb and Fe biogeochemistry of the ocean) and as tracers of the past operation of the ocean (e.g., Cd in corals and foraminifera).
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 and Pb isotopes in ice cores, varved sediment cores, coral cores, and in the ocean. We have measured Pb in surface and deep seawater samples for the past 30 years, and we can estimate Pb for the preceding two centuries using Pb in annually-banded corals from Bermuda. The emitted 206/207, 208/207 and 206/204 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 establishing a unique combination of isotope ratios. Varved sediment cores from Rhode Island and British Columbia show the regional differences in Pb emissions.
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. Boyle’s Trace Metal Group has developed small-volume (1.3 ml) methods for the analysis of iron in seawater using collision-cell plasma mass spectrometry. In addition, they have developed methods for the distinction of colloidal (0.02-0.4 µm) iron from soluble iron (<0.02 µm).
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, Boyle’s group 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).
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. The Cr-isotope system will
We are completing our participation in a ten-year NSF-funded center C-MORE (Center for Microbial Oceanography Research and Education), where Boyle’s group works with marine biologists and atmospheric dust scientists to unravel the relationship between dust, iron in the ocean, and nitrogen fixation in the central North Pacific and South Pacific. C-MORE is 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. Three years ago, Rick Kayser and Jong-Mi Lee joined C-MORE colleagues on a research cruise from Chile to Easter Island; Jessica Fitzsimmons has shown that there is hydrothermal iron in the deep eastern South Pacific. Two years ago, Abigail Noble, Gonzalo Carrasco, Simone Moos, Jessica Fitzsimmons and Rick Kayser joined C-MORE colleagues to “Occupy HOT” with a nearly continuous time series of samples during the summer months. This past summer, Chris Hayes went out to HOT for two weeks to continue work on Fe, Th, and dust fluxes.
GEOTRACES is an international program to study trace elements andGEOTRACES is an international program to study trace elements and isotopes in the global ocean. Many properties that are important either directly to biogeochemical cycling (e.g. Fe, Zn, Cd, Co) or to tracing biogeochemical cycles in past oceans (e.g. Cd, Th-230, Pa-231, Be-10) have very limited global ocean data to decipher the processes that control them. GEOTRACES will enlist the efforts of the major scientific sea-going nations of the world to collect 10-15 sections throughout the world ocean during the next 10-12 years.
Two intercalibration cruises were completed (Atlantic, June 2008; Pacific, May 2009). Our group, along with Bill Jenkins (WHOI) and Greg Cutter (ODU) were PIs on the lead proposal to undertake the first U.S. GEOTRACES zonal North Atlantic section that began with a 3 week cruise (Lisbon-Cape Verde Islands) in October 2010 and finished in November-December 2011with a 37-day cruise from Woods Hole to Bermuda to the Cape Verde Islands. In 2013, we obtain samples for Pb from the EPZT (Eastern South Pacific Zonal Transect) from Peru to Tahiti. This summer (2015), graduate student Simone Moos is on the USCG icebreaker Healy sectioning from Alaska to the North Pole. Our lab is measuring Pb and Pb isotopes from samples from those cruises. Postdocs Yolanda Echegoyen-Sanz, Abigail Noble, and Cheryl Zurbrick have been working on the samples collected during these cruises.
We have also measured Pb and Pb isotopes on samples from the Japanese GEOTRACES transect in the Indian Ocean and are doing the same for samples from the French GEOVIDE section in the northern North Atlantic Ocean.
CENSAM (Center for Environmental Sensing and Modeling) is a joint Singapore-MIT project. We are working a subproject to generating anthropogenic chemical histories (Pb, Pb isotopes, Cd) and paleoclimate records from corals in the Singapore/Indonesian/Indian Ocean region, and investigate the behavior of trace metals (concentration, speciation, and isotopes) in Singapore coastal waters. Postdocs Intan Nurhati, Gonzalo Carrasco, Kuanbo Zhou and graduate student Mengli Chen are in residence in Singapore (NUS and NTU) and are in charge of coral collection and sampling and developing models for Pb transport. Mengli and Intan have been at MIT making measurements of Pb, Pb isotopes, and Ba from Singapore corals. The group has recently setup a clean lab for sample processing and developing multicollector ICPMS methods on the instrumentation of Prof. Wang at EOS-NTU. Our graduate student Jong-Mi Lee has Pb isotope records that show an unexpected Pb isotope signature in Singapore waters, and Mengli and Ed have taken sediment cores in Singapore reservoirs to try to track down the source of this signature. Mengli has also studied a 150 year record of Pb, Pb isotopes, and Cd off the coast of Vietnam in the South China Sea.
The Kuwait Foundation for the Advancement of Science (KFAS) is supporting a project between our group and a group at the Kuwait Institute for Scientific Research (KISR) to establish histories of metals (Pb, Pb isotopes, Cd) and organic pollutants (e.g. PAH) for the Northern Arabian Gulf. We are in the final stages of finishing up the work on this project, with submission of one paper and preparation of a second. We have collected seawater samples, sediment cores and surface sediment samples, and corals in order to establish the history of these pollutants during the past 50-200 years. Postdoc Gonzalo Carrasco and Joint Program graduate student Ning Zhou is working with Ed on this project together with our colleagues in Kuwait, Bondi Gevao, Kharlid Matrouk, Saif Uddin, Lulwa Ali, Abdul Al-Ghadban, and Abdullah Aziz.