Photo of Ken on the deck of the RV Kilo Moana during the Bering Sea cruise 2003, enjoying the sun and watching walruses on the rocky beach.
Ken watching the Walruses,
Bering Sea 2003

Ken Bruland

Distinguished Professor
Ocean Sciences/Crown College
 
Ocean Sciences Department
University of California
1156 High Street
Santa Cruz CA 95064
831-459-4587 (office)
831-459-2682 (lab)
831-459-4882 (fax)
photo of Ken and Geo bringing another water sample onboard using a General Oceanics 30 liter GO-Flo bottle on the RV Pt. Sur, IMUP 2004
Ken and Geo sampling onboard
the RV Pt. Sur,
IMUP 2004

Welcome to Ken's Research Lab web site.

Ken's research involves investigating trace metal interactions with biotic and abiotic components in natural waters.

Ken's research group actively develops new instrumentation and analytical techniques to detect trace metals in natural waters at ultra-low concentrations. We apply these and pre-existing methods to better understand the factors affecting trace metal cycling and productivity in the world's oceans, bays and estuaries.

Our efforts include many oceanic and near-shore research cruises in many different areas of the world from here in our backyard Monterey Bay to the oceanic gyres.

Over the last several years we also have been involved with the SAFe and GEOTRACES intercalibration projects and are continuing to provide reference sea water samples to the international oceanographic trace metal community. Ken has been working with participants to arrive at consensus values for many key GEOTRACES elements in sea water ranging from open ocean to coastal concentrations. These samples and the anonymous international database that Ken maintains are proving extremely valuable to advance our collective understanding of the worlds oceans.

diagram showing the interactive influences between Trace metals and Phytoplankton
Interactive influences between trace metals and phytoplankton

Research Focus

An exciting research frontier in ocean sciences involves the role of micronutrient trace metals such as iron, manganese, zinc, and cobalt in affecting the structure and function of plankton communities. Certain bioactive trace metals - in particular iron - can influence marine phytoplankton at the molecular, cellular, community and ecosystem levels. In turn, the oceanic distributions, cycling and chemical speciation of these key trace metals are strongly influenced by the activities of the planktonic communities (Bruland et al. 1991; Bruland and Lohan 2004). The figure below (modified after a figure of Bill Sunda) depicts these interactive influences of trace metals and phytoplankton.

Of particular importance is the critical roles trace metals such as iron play as biolimiting micronutrients. This is especially relevant in certain oceanic areas where macronutrients are provided to the surface waters by upwelling or vertical mixing at high rates without an adequate external source of the micronutrient iron. The low concentration and supply of iron in remote high-nutrient, low-chlorophyll (HNLC) regions has resulted in the Fe-hypothesis, whereby the lack of iron limits large phytoplankton such as diatoms and results in ecosystems dominated by picoplankton (Martin et al. 1991; Price et al. 1994). These picoplankton-dominated systems are tightly coupled with their protozoan grazers and tend to have a low and relatively constant biomass (Banse and English 1994). The addition of the micronutrient Fe to these HNLC areas can cause depletion of the macronutrients and result in a bloom by larger phytoplankton such as diatoms.

Iron Availability in Upwelling Regimes

Recently, we have shown that iron (Fe)-limitation can be important in macronutrient-rich coastal upwelling regimes. Northwesterly winds along the coast of central California result in wind-driven coastal upwelling that brings colder, nutrient-rich water to the surface. This process is most intense during the spring and summer. The large flux of the essential plant macronutrients nitrate, phosphate, and silicic acid can allow extensive phytoplankton blooms to occur that may extend tens to hundreds of kilometers offshore. Phytoplankton blooms occur when nutrient-replete conditions promote rapid algal growth rates temporarily uncoupled from grazing pressure. Large diatoms tend to dominate the biomass in phytoplankton blooms that develop in these coastal upwelling regimes, and it has been argued that diatom-driven new production efficiently fuels the food chains that support coastal fisheries, seabirds, and marine mammals.

The potential productivity associated with upwelling centers, however, is not always realized. Recent studies (Hutchins and Bruland 1998; Hutchins et al. 1998; Bruland et al. 2001; Firme et al. 2003) have demonstrated that the supply of iron, a key micronutrient, plays a critical role in controlling phytoplankton blooms in these coastal upwelling regimes. Iron-rich upwelling regions experience extensive blooms of diatoms that deplete available macronutrients; while in iron-poor areas, the biomass of phytoplankton is greatly reduced and high concentrations of unutilized macronutrients persist. Thus, understanding the supply of iron is a key for understanding the variability in productivity along the California coast.

diagram comparing upwelling over narrow and broad continental shelves
Upwelling over narrow verses broad continental shelves.

If adequate iron is available, then nitrate becomes the key nutrient that limits bloom development. If, however, only a small amount of iron is available, then iron can be the key nutrient that limits bloom development and can result in water low in phytoplankton biomass, but still rich in unutilized macronutrients such as nitrate. The major source of iron to the central California upwelling regime originates from river discharge of suspended sediments. The width of the continental shelf plays a role because when a sufficiently broad continental shelf is present, much of the winter fluvial (from rivers) discharge of suspended sediment is rapidly deposited as "mud belts" on the shelf at depths of 40 to 100 meters; thus a relatively broad continental shelf can act as an “iron trap” for these fluvial inputs. This is important since in the winter when fluvial input is the greatest, upwelling is at a minimum; and in the spring and summer months when upwellling is most intense, the direct river input is neglible. When coastal upwelling of macronutrient-rich water takes place over these broad shelf regions, elevated concentrations of iron can be entrained resulting in water enriched with both macronutrients and iron (see the upper figure to the left). In contrast if a broad shelf is lacking, then the macronutrients are upwelled without an extra source of iron (lower figure).

SeaWifs image showing chlorophyll distribution measured using ocean color in surface waters off the central California Coast
SeaWIFS image showing surface chlorophyll concentrations
in squirts and eddies off the central California coast.
(Provided by Raphael Kudela)

In the central California studies we have shown that the iron input to upwelling waters varies markedly both spatially and temporally, and can be characterized by two end-member regimes. One end-member, including Monterey Bay and extending north to Pt. Reyes, is an Fe-replete regime where upwelling occurs over a relatively broad continental shelf (with "mud belts" supplied each year with fresh winter flood deposits) that results in upwelled waters with high concentrations of dissolved and leachable particulate iron (> 10 nM). In these Fe-replete regions, extensive blooms of large diatoms rapidly deplete the macronutrients resulting in high chlorophyll concentrations as shown in the SeaWIFS image to the left. The other end-member, located off the Big Sur coast, is an Fe-deplete regime where upwelling is focused offshore of a narrow continental shelf. Freshly upwelled waters in the Big Sur region are characterized by low dissolved and leachable particulate Fe (<1 nM). Extremely low iron results in unutilized nitrate and silicic acid, and a low abundance of large diatoms characterize surface waters in these Fe-deplete regions. These areas represent coastal upwelling, high-nutrient, low-chlorophyll (HNLC) systems limited by the micronutrient iron.

The development of this website and most of the research described here was supported by grants from the National Science Foundation.
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