OCEANIC BIOGEOCHEMISTRY

Background: The cycling of a number of elements is tied to biological productivity, plant production, in the oceans. For example, phosphorus and nitrogen are essential to biological productivity in the oceans and in turn have their distributions within the water column strongly affected by plant and animal activity. Additionally, carbon dioxide is absorbed from the atmosphere and into the oceans by physical processes, but also by the surface ocean biological "pump" which draws carbon out of the water/atmosphere and into organic matter which settles into the deep sea. Understanding the changes that might occur in global element cycles with climate change includes understanding the behavior of the marine biotic system and changes in plant productivity.

    Also, the exchange of CO₂ between the oceans and atmosphere is influenced by the ratio of organic carbon (take up CO₂) to calcite (release CO₂) production in the surface ocean and the consequent organic carbon to calcite flux ratio of particles settling into the deep sea.  The particle ratio depends on the composition of plankton communities living in the surface ocean, and these respond primarily to chemical stimuli (essential nutrients and trace elements) which control the degree to which communities are composed of carbonate or non-carbonate (opal) producers.

WHAT WE ARE DOING: Understanding how global biogeochemical cycles might change requires that we examine the behavior of these cycles as they respond to a variety of conditions different from those we see on earth today. We have developed means for reconstructing oceanic biological activity (open ocean biological productivity) over time using benthic (bottom dwelling organism) microfossils recovered from deep ocean sediments. Our technique have application to the global ocean and allows us to examine the behavior of the marine biosystem over longer stretches of time and under environmental conditions different from the present. Currently, we are concentrating on reconstructing marine biological productivity in the tropical oceans during the last 150,000 years. This is a time period encompassing large global environmental changes.

   Additionally, we have developed new techniques for reconstructing past fluxes of biogenic components to the deep sea so that we can evaluate changing organic carbon and calcite flux ratios.  This work involves integration of the microfossil record with chemical, isotopic and radiochemical analyses of deep sea sediments.

   In pursuing these research goals we have developed a new inorganic isotope research laboratory which includes a Thermofinnigan MAT253 stable isotope ratio mass spectrometer and an ELEMENT II ICP-MS.

LINK TO CLIMATE CHANGE GLOBAL CLIMATE

SEABED BIOGEOCHEMISTRY: The deep ocean bottom is a mysterious place, much of it like a desert in that there is almost nothing to eat. It is dark and cold and nutrition mostly settles as scraps from the fertile, sunlit, ocean surface. What drifts down drives biogeochemical cycles within the sediments that are slowly accumulating in the abyss. These biogeochemical cycles affect the characteristics of the deep sea sediments and the record of global change that they retain. The biogeochemical cycles are probably linked to the activity of bottom dwelling animals which burrow into the seabed, hoard and transport food and plow through the sediments in search of a meal. These organisms redistribute the labile organic matter that provides energy for the biogeochemical cycles and also change chemical concentration profiles by burrowing and mixing the sediments. This alters the flux of chemicals into, and out of, the seabed.

WHAT ARE WE DOING? Our group has examined the distribution of one benthic animal, benthic FORAMINIFERA, within deeper marine sediments in relation to larger organism structures and chemical properties in the sediments. Our purpose is to define the relationship of these micro-organisms to their chemical and biological surroundings. The FORAMINIFERA produce skeletons that become part of the deep ocean record of the Environment and Global Change. In examining the ecology of the benthic organisms we seek an understanding of how exactly their existence is tied to the larger environmental events that their skeletal remains record for us within the sediments. Our work entails sampling the distribution of the micro-organisms in relation to sedimentary features and chemistry on finer and finer spatial scales to capture the environmental field that the organisms actually sense and respond to.

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