Mixing and biological production at eddy margins in the eastern Gulf of Alaska

Abstract We performed a multi-day shipboard experiment in June 2001 to test whether combining water from within an anticyclonic mesoscale eddy in the eastern Gulf of Alaska with water from outside could result in enhanced phytoplankton growth and to determine how mixing might influence planktonic assemblages. Initially, the eddy had lower standing stocks of algal pigments (chlorophyll a [chl a ] and accessory pigments), nutrients, phytoplankton, and particulate organic carbon/nitrogen compared to waters outside of the eddy. The eddy possessed a greater diversity and abundance of coastal diatoms while the outside waters had a greater proportion of oceanic species, including the endemic pennate diatom, Nitzschia cylindroformis . After one week of incubation, rates of primary production were significantly higher in the mixed water compared to both the eddy and outside treatments. Pigment concentrations (except chl c 3 , alloxanthin, and zeaxanthin) and the proportion of large diatoms (mainly Pseudo-nitzschia spp.) and heterotrophic dinoflagellates were greater in the mixed water than would be expected from the simple combination of inside and outside waters. Nutrient limitation (most likely by trace metals) appeared to be less severe in the mixed water. Chl a was enhanced in the mixed water, particularly when compared to the eddy water. The mixing of eddy and outside water masses stimulated primary production by ∼20%, but more importantly, the mixing resulted in a distinct planktonic assemblage. The biomass enrichment was short-lived, indicating that the maintenance of elevated chl a would require further mixing events in a physical setting that also permits an accumulation of biomass. We note that submesoscale processes, including the intensification of ageostrophic circulation that elicits strong vertical mixing in the presence of strain, might explain observed patterns of high phytoplankton standing stocks at the inner edges of Haida eddies in the field.

[1]  R. Barlow,et al.  Phaeopigment distribution during the 1990 spring bloom in the northeastern Atlantic , 1993 .

[2]  R. Margalef.  Life-forms of phytoplankton as survival alternatives in an unstable environment , 1978 .

[3]  Matthew T. Wilson,et al.  Acoustic detection of mesoscale biophysical features in the Shelikof sea valley, and their relevance to pollock larvae in the Gulf of Alaska , 1996 .

[4]  J. Yoder,et al.  Pumping of nutrients to ocean surface waters by the action of propagating planetary waves , 2001, Nature.

[5]  L. Prieur,et al.  Phytoplankton dynamics associated with a geostrophic front: Ecological and biogeochemical implications , 1994 .

[6]  H. Saito,et al.  Responses of microzooplankton to in situ iron fertilization in the western subarctic Pacific (SEEDS) , 2005 .

[7]  W. Crawford,et al.  Mesoscale eddy aswirl with data in Gulf of Alaska , 1999 .

[8]  John P. Ryan,et al.  Enhanced chlorophyll associated with tropical instability waves in the equatorial Pacific , 2001 .

[9]  A. Tamhane,et al.  Multiple Comparison Procedures , 1989 .

[10]  C. M. Yentsch,et al.  Thalassiosira oceanica and T. pseudonana: two different photoadaptational responses , 1987 .

[11]  W. Crawford.  Physical Characteristics of Haida Eddies , 2002 .

[12]  William R. Crawford,et al.  Currents in Haida Eddies , 2005 .

[13]  B. C. Booth,et al.  Nanoplankton species predominant in the subarctic Pacific in May and June 1978 , 1982 .

[14]  Peter Franks,et al.  Phytoplankton blooms at fronts: Patterns, scales, and physical forcing mechanisms , 1992 .

[15]  G. Forster,et al.  Summer phytoplankton blooms and red tides along tidal fronts in the approaches to the English Channel , 1975, Nature.

[16]  W. Broenkow,et al.  Vertex: phytoplankton/iron studies in the Gulf of Alaska , 1989 .

[17]  W. K. Johnson,et al.  Iron transport by mesoscale Haida eddies in the Gulf of Alaska , 2005 .

[18]  D. Hutchins,et al.  Iron-limited diatom growth and Si:N uptake ratios in a coastal upwelling regime , 1998, Nature.

[19]  E. Lessard,et al.  Species-specific grazing rates of heterotrophic dinoflagellates in oceanic waters, measured with a dual-label radioisotope technique , 1985 .

[20]  P. Bolt,et al.  Phagotrophy and fecal pellet production by an athecate dinoflagellate in Antarctic sea ice , 1990 .

[21]  A. Mahadevan,et al.  Comment on "Eddy/Wind Interactions Stimulate Extraordinary Mid-Ocean Plankton Blooms" , 2008, Science.

[22]  P. Harrison,et al.  Physical processes that enhance nutrient transport and primary productivity in the coastal and open ocean of the subarctic NE Pacific , 2005 .

[23]  M. Chierici,et al.  Biogeochemical evolution of the carbon dioxide system in the waters of long-lived mesoscale eddies in the Northeast Pacific Ocean , 2005 .

[24]  E. Woodward,et al.  Optimization Of The Indophenol Blue Method For The Automated-Determination Of Ammonia In Estuarine Waters , 1983 .

[25]  David Archer,et al.  Modeling the impact of fronts and mesoscale circulation on the nutrient supply and biogeochemistry of the upper ocean , 2000 .

[26]  Adrian P. Martin.  Phytoplankton patchiness: the role of lateral stirring and mixing , 2003 .

[27]  A. Mcintyre,et al.  Determination of organic carbon and nitrogen in marine sediments using the Carlo Erba NA-1500 analyzer , 1990 .

[28]  Andrew C. Thomas,et al.  A census of oceanic anticyclonic eddies in the Gulf of Alaska , 2008 .

[29]  William R. Crawford,et al.  The influence of coastal origin eddies on oceanic plankton distributions in the eastern Gulf of Alaska , 2005 .

[30]  W. K. Johnson,et al.  Patch evolution and the biogeochemical impact of entrainment during an iron fertilisation experiment in the sub-Arctic Pacific , 2006 .

[31]  R. Barlow,et al.  Pigment signatures of the phytoplankton composition in the northeastern Atlantic during the 1990 spring bloom , 1993 .

[32]  P. Harrison,et al.  Comparison of factors controlling phytoplankton productivity in the NE and NW subarctic Pacific gyres , 1999 .

[33]  P. Harrison,et al.  Evolution of the phytoplankton assemblage in a long-lived mesoscale eddy in the eastern Gulf of Alaska , 2011 .

[34]  D. Anderson,et al.  WIDESPREAD PHAGOCYTOSIS OF CILIATES AND OTHER PROTISTS BY MARINE MIXOTROPHIC AND HETEROTROPHIC THECATE DINOFLAGELLATES 1 , 1996 .

[35]  Susanne Menden-Deuer,et al.  Carbon to volume relationships for dinoflagellates, diatoms, and other protist plankton , 2000 .

[36]  P. Harrison,et al.  Macronutrient dynamics in an anticyclonic mesoscale eddy in the Gulf of Alaska , 2005 .

[37]  A. Tsuda,et al.  Phytoplankton processes during a mesoscale iron enrichment in the NE subarctic Pacific: Part I-Biomass and assemblage , 2006 .

[38]  James K. B. Bishop,et al.  Transmissometer measurement of POC , 1999 .

[39]  James C. McWilliams,et al.  Mesoscale to Submesoscale Transition in the California Current System. Part II: Frontal Processes , 2008 .

[40]  P. Boyd,et al.  Importance of stirring in the development of an iron-fertilized phytoplankton bloom , 2000, Nature.

[41]  M. Behrenfeld,et al.  Abandoning Sverdrup's Critical Depth Hypothesis on phytoplankton blooms. , 2010, Ecology.

[42]  Shigenobu Takeda,et al.  Influence of iron availability on nutrient consumption ratio of diatoms in oceanic waters , 1998, Nature.

[43]  A. Tamhane,et al.  Multiple Comparison Procedures , 2009 .

[44]  T. Weingartner,et al.  Satellite and hydrographic observations of eddy‐induced shelf‐slope exchange in the northwestern Gulf of Alaska , 2003 .

[45]  Nicholas R. Bates,et al.  Eddy/Wind Interactions Stimulate Extraordinary Mid-Ocean Plankton Blooms , 2007, Science.

[46]  M. Brzezinski,et al.  THE Si:C:N RATIO OF MARINE DIATOMS: INTERSPECIFIC VARIABILITY AND THE EFFECT OF SOME ENVIRONMENTAL VARIABLES 1 , 1985 .

[47]  S. L'Helguen,et al.  Nitrogen Uptake by Phytoplankton in a Shallow Water Tidal Front , 2000 .

[48]  R. R. Strathmann,et al.  ESTIMATING THE ORGANIC CARBON CONTENT OF PHYTOPLANKTON FROM CELL VOLUME OR PLASMA VOLUME1 , 1967 .

[49]  G. Borstad,et al.  Biological Fronts in the Strait of Georgia, British Columbia, and Their Relation to Recent Measurements of Primary Productivity , 1981 .

[50]  E. Steemann Nielsen,et al.  The Use of Radio-active Carbon (C14) for Measuring Organic Production in the Sea , 1952 .

[51]  P. Brickley,et al.  Impact of Haida Eddies on chlorophyll distribution in the Eastern Gulf of Alaska , 2005 .

[52]  B. C. Booth.  Size classes and major taxonomic groups of phytoplankton at two locations in the subarctic pacific ocean in May and August, 1984 , 1988 .

[53]  K. Mann,et al.  Dynamics of marine ecosystems:biological-physical interactions in the oceans , 1992 .

[54]  Andrew G. Dickson,et al.  Protocols for the Joint Global Ocean Flux Study (JGOFS) Core Measurements , 1996 .

[55]  W. K. Johnson,et al.  Size-fractionated iron concentrations in the northeast Pacific Ocean : distribution of soluble and small colloidal iron , 2001 .

[56]  F. Whitney,et al.  The uptake and export of silicon and nitrogen in HNLC waters of the NE Pacific Ocean , 2005 .

[57]  M. Estrada,et al.  Losses of chlorophylls and carotenoids in aqueous acetone and methanol extracts prepared for RPHPLC analysis of pigments , 2001 .

[58]  A. Kopylov,et al.  Plankton distribution associated with frontal zones in the vicinity of the Pribilof Islands , 2002 .

[59]  K. Bruland,et al.  Sampling and analytical methods for the determination of copper, cadmium, zinc, and nickel at the nanogram per liter level in sea water , 1979 .

[60]  S. Strom,et al.  Phytoplankton blooms are strongly impacted by microzooplankton grazing in coastal North Pacific waters , 2001 .

[61]  C. L. Leonard,et al.  Mesoscale Eddies Drive Increased Silica Export in the Subtropical Pacific Ocean , 2007, Science.

[62]  D. Mackas,et al.  Zooplankton distribution and dynamics in a North Pacific Eddy of coastal origin: II. Mechanisms of eddy colonization by and retention of offshore species , 2005 .

[63]  K. Mann,et al.  Dynamics of Marine Ecosystems: Biological and Physical Interactions in the Oceans , 1997 .

[64]  G. Hasle,et al.  Nitzschia cylindroformis sp. nov., a common and abundant nanoplankton diatom of the eastern subarctic Pacific , 1984 .

[65]  S. Fitzwater,et al.  Metal contamination and its effect on primary production measurements1 , 1982 .

[66]  Andrew C. Thomas,et al.  Mesoscale eddies dominate surface phytoplankton in northern Gulf of Alaska , 2007 .

[67]  P. Harrison,et al.  Sinking rate response to depletion of nitrate, phosphate and silicate in four marine diatoms , 1982 .

[68]  K. Johnson,et al.  Influence of Rossby waves on nutrient dynamics and the plankton community structure in the North Pacific subtropical gyre , 2004 .

[69]  F. Whitney,et al.  Structure of Haida Eddies and Their Transport of Nutrient from Coastal Margins into the NE Pacific Ocean , 2002 .

[70]  Deborah K. Steinberg,et al.  Revisiting Carbon Flux Through the Ocean's Twilight Zone , 2006, Science.