All life on earth requires nutrients to survive. Nitrogen and phosphorus are essential macronutrients for the growth of aquatic plants and animals. Some phytoplankton (such as diatoms) also requires silicon for building their cell walls. Metals, such as iron and molybdenum, are needed in much smaller amounts and are considered micronutrients. Excess input of nutrients to the environment, often induced by human activity, can cause algae blooms resulting in eutrophication in the aquatic ecosystem.

The OCED's nutrient biogeochemistry program utilizes state-of-the-art equipment and techniques, many of which were developed in-house to study nutrient dynamics in coastal and open ocean environments. The field programs focus on the nutrient dynamics coupled with carbon and oxygen cycles in open oceans. In coastal environments, we study the role of nutrient availability in ecosystem functioning.

Current projects being conducted by the Nutrient Biogeochemistry program are:

1. In collaboration with PMEL's nutrient group, we conducted high quality shipboard nutrient measurements in the Go-Ship/Repeat Hydrography program. Nutrient data are essential in estimating anthropogenic carbon in the ocean and in studying global biogeochemical cycles. The figures show recent measurements of phosphate, nitrate and silicate along the A16 cruise track and display of the remineralization signals increasing with age of deep water masses. Biological uptake results in low nutrients in surface waters. Recently ventilated Labrador Sea water and Upper North Atlantic Deep Water have relatively lower nutrient content because of younger water masses (~ 100 years). Antarctic Intermediate Water is evident as a high nutrient tongue extending to 25ºN at approximately 1000 m depth. The old Antarctic Bottom water in South Atlantic has the highest nutrients content and reaches the Mid-Atlantic Ridge around the equator. Concurrent measurements of DIC, nutrients, oxygen and CFC as well as physical parameters in repeat hydrography program provide valuable information on ocean circulation and biogeochemical processes in the Atlantic Ocean.

2. We have performed, in collaboration with the Florida Bay and FACE programs, high quality nutrient measurements for the the water quality monitoring program in south Florida coastal waters.

3. Utilizing sequential extraction technique and sorption isotherm experiments, the nutrient group studied the sediment-water exchange of phosphorus in the Florida Bay and the role of sediment resuspension in controlling this limiting nutrient. A solid understanding of phosphorus cycling between water and sediment is needed in order to predict the effect it will have on ecosystem function and the consequences on environmental change.

4. We have developed analytical methods for low-level nutrient measurements using liquid waveguide and other novel techniques. Such capability are needed because standard methods do not achieve the detection limits required for measurements in oligotrophic waters (e.g., typical coral reef habitat, open ocean surface waters) or the high spacial resolution underway measurements required for oceanic surface process study (e.g., tracer tracking, plum mapping).