Western Arctic Shelf-Basin Interactions (SBI) Project

Dennis Hansell (University of Miami, Rosenstiel School of Marine and Atmospheric Science) and Nick Bates (Bemuda Biological Station)

Collaborative Research: Transport and Transformations of Carbon and Nitrogen in the Western Arctic Ocean: A Contribution to the SBI Project

The Western Arctic Shelf-Basin Interactions (SBI) project focuses on shelf, shelf break and upper-slope water mass and ecosystem modifications, material fluxes and biogeochemical cycles. The geographical focus is on the Chukchi and Beaufort Seas and adjacent upper slopes, with the aim of generalization of the results into Pan Arctic and global models. The overarching goal of the SBI project is to understand the physical and biogeochemical processes that link the Arctic shelves, slopes, and deep basins. Relevant to this proposal, the SBI project will focus on a) biogeochemical modifications of Pacific water over the Beaufort and Chukchi shelf and slope regions, with emphasis on carbon and nitrogen; and b) comparative analysis of the findings over the broad Chukchi shelf and narrow Beaufort shelf and adjacent slopes to facilitate integration of the Western Arctic into a Pan-Arctic perspective.

We will support the goals of SBI by evaluating the processes of carbon and nitrogen transport, exchanges and transformations in the regions of interest. Our specific interests will be: a) determination of mass transport and fate of carbon and nitrogen associated with the volume transports calculated by SBI collaborators; b) interpretation of carbon and nitrogen spatial distributions and temporal variability relative to biological and physical conditions; c) evaluation of partitioning of organic matter between dissolved and particulate phases; d) determination of net community production and it's fate as DOM, suspended POM, and sinking POM; e) determination of C:N stoichiometry as a complement to biological studies, particularly in relation to community structure and seasonal progression of intense phytoplankton blooms in the Chukchi and Beaufort Seas; and f) evaluation of the contribution of DOM vs. POM to apparent oxygen utilization (AOU) development in the Arctic halocline and export from the shelf.

We will measure the full suite of carbon and nitrogen variables in survey mode. These include dissolved organic carbon (DOC), dissolved inorganic carbon (DIC), as well as dissolved organic nitrogen (DON). Dissolved inorganic nitrogen (DIN), a required variable, will be measured by the Category 2 hydrographic team contracted by SBI. We will also measure alkalinity to aid in identification of water masses. DOC, DIC, total alkalinity, and seawater pCO2 will be determined at sea. DON, PON, and POC will be analyzed at our shore labs. We require that 4 individuals from our groups (2 for organic variables and 2 for inorganic variables) join each of two 6-week process cruises each summer (2002 and 2004). Synthesis of data will progress throughout the five year project, culminating in the overarching final year synthesis. We anticipate ongoing synthesis and modeling collaborations with other funded SBI groups, including the physical oceanographic and tracer groups, the service groups and biological studies groups.

Rodger Harvey (University of Maryland) and Ron Benner (University of South Carolina)

Collaborative Research: Biogeochemical Cycling of Particulate and Dissolved Organic Matter in the Arctic Ocean using Molecular Markers

We will investigate marine and terrestrial molecular organic markers in particulate material DOM and surface sediments, its transformation in the water column and sediments, and transport across the shelf-basin boundary. We will analyse 60 samples per cruise to include POC/PN, fatty acids, sterols, alcohols,, alkanes/alkenes, hopanes (bacterial), triterpenes (higher plant markers), neutral sugars and amino sugars. In addition we will include total protein & amino acids for all particulate samples. A companion set of samples (60) will be collected for DOM characterization. These samples will be analyzed for DOC, neutral sugars, amino sugars, amino acids, and lignin-derived phenols. This sample number can be partitioned between survey and experimental work as needed. Our sediment samples are being used for two purposes. The first will be to examine molecular organic markers in upper sediment layers as an integrator of organic fluxes which we will compare with water column samples. This will provide information on both he preservation of organic matter, its processing in surface sediments and variability in the types of organic matter reaching underlying sediments. The second will be the examination of redox-sensitive elements with increasing sediment depth to test the hypothesis that sediments in some areas may have experienced episodic inputs of labile organic matter which are not be reflected in total organic carbon values. Two set of measures requires two cores.

David Kadko (University of Miami, Rosenstiel School of Marine and Atmospheric Science)

Proposal Title: Investigation of the Rate of Shelf-Basin Interaction in the Western Arctic Ocean Using Radium Isotopes: SBI PHASE II

The largely landlocked Arctic Ocean receives input from the Pacific and Atlantic Ocean, and from rivers draining the surrounding continents. These inflows are important sources of salt, heat, nutrients, sediment and organisms to the central basin. With the exception of a portion of the Atlantic contribution, these inputs must cross continental shelves where they are significantly modified by benthic, water column, air/sea and sea/ice interactions. There are therefore significant biogeochemical exchanges between the shelves and basins, but we currently lack the information necessary to quantify these exchanges. To address this issue, as part of the Western Shelf-Basin Interaction (SBI) PHASE II program, we will apply an isotopic tracer technique for elucidating the pathways and rate of exchange between the Arctic shelves and the Arctic Ocean interior. The technique utilizes the measurement of the water column ratio of two naturally occurring radium isotopes 228Ra/226Ra. Because 228Ra (T1/2 = 5.77 y) is derived solely through input from shelf sediments, it is an unambiguous marker of shelf water. Its relative distribution in shelf and basin water is therefore very valuable in assessing the degree of shelf-basin interaction. This technique is mature, having been utilized in shelf-basin exchange investigations elsewhere, and pilot results from SBI PHASE I have clearly indicated this tracer's utility in the western Arctic Ocean study. Tracer data collected by ship transects during the field program will be analyzed within the context of modeling studies by other investigators that are aimed at understanding offshore transport, including the role and formation of eddies in this process. Where appropriate, the short-lived 224Ra (T1/2= 3.64d) will be measured at sea to supplement our data set. Radium tracer data will also be collected autonomously from floating drifters (if available) and moored arrays (if suitable moored instrumentation is made available in SBI) that are designed to study the role of eddies in the western Arctic shelf-basin interaction and time-variability of shelf currents.



Robert Pickart, Principal Investigator (Woods Hole Oceanographic Institution)

Dynamics of Exchange in the Beaufort Sea Boundary Current System: Implications for Interior Ventilation

OBJECTIVES:

· To quantify the mean and seasonally varying transport, structure, and water mass content of the boundary current system downstream of the Chukchi Sea outflow points.

· To determine the nature and cause of the mesoscale variability of the boundary current, and assess the impact of the variability on the cross-stream exchange of mass and properties.

· To identify the dynamics of the secondary circulation.

· To elucidate the source of the interior eddies by comparing the seasonally changing boundary current water to the characteristics of the observed mid-basin eddy field.

We will deploy six moorings across the Beaufort shelfbreak and upper slope, approximately 150 km east of Barrow Canyon. These will be serviced annually during the mooring cruises. Each mooring consists of a bottom-mounted upward-looking ADCP, and a profiling CTD. This will provide vertical profiles of velocity (once per hour) and temperature/salinity (four times daily).



Barry Sherr and Ev Sherr, (Oregon State University) and Carin Ashjian and Robert Campbell (Woods Hole Oceanographic Institution)

Collaborative Research: Mesozooplankton-Microbial Food Web Interactions in the Arctic Ocean

A central goal of the Shelf-Basin Interactions (SBI) program is to understand the processes affecting carbon transformations and fluxes within and between Arctic shelf and basin ecosystems, and how climate change might impact these processes. The cycling of carbon in Arctic shelf and basin habitats depends on the structure and functioning of the food webs of these regions. In the pelagial, both micro- and meso- zooplankton are significant consumers of primary production. The partitioning of primary production between the fractions remaining in the water column or sedimenting to the benthos (where organic matter is less available for export from the shelf) can be greatly affected by the relative grazing rates of microzooplankton versus mesozooplankton herbivores. Microzooplankton grazing dampens export flux, while mesozooplankton grazing enhances it. The primary focus of our proposed collaborative project is an analysis of the impact of microzooplankton and mesozooplankton grazers on the fluxes and exchanges of carbon within the oceanic waters of the Canada Basin and the shelf waters of the Chukchi/Beaufort Seas. We will use standard methods and experimental protocols to determine the standing stocks and size structures of microzooplankton, phytoplankton, and mesozooplankton assemblages, to measure growth (microzooplankton) and reproduction (mesozooplankton) rates, to measure grazing rates of heterotrophic protists and dominant mesozooplankton in the two regions, and to identify mesozooplankton that are sentinel species of Arctic change. Our collaborative study will explicitly address trophic linkages previously unexplored in this region of the Arctic. We hypothesize that changing ecosystem structure, such as might occur during climate change, will alter the role of these trophic interactions in the utilization and cycling of carbon in arctic shelves and basin systems.

We propose participation in the four process cruises of the SBI Phase II program. The planned cruise schedules of May-June and July-August will permit us to work in contrasting scenarios of ice cover, and importance of ice algae versus phytoplankton in primary production, during early summer compared to late summer. Since we plan a comparison of the phytoplankton – microzooplankton – mesozooplankton trophic coupling in shelf versus basin systems, we will carry out a full set of analyses (standing stock determinations and rate measurements) at a number of stations in both basin and shelf regions of the SBI-II study area. Abundances and rate measures will be combined to determine relative mesozooplankton and microzooplankton grazing impacts. The research proposed here addresses major objectives of the SBI-II program: 'Assessment of relative importance of top-down as compared to bottom-up controls over pelagic-benthic coupling and carbon partitioning among different trophic levels' and 'Assessment of food web changes consequent to the impacts of changing ice cover and hydrographic parameters on biogeochemical fluxes.' This project will provide rate measurements for microzooplankton and mesozooplankton grazing and reproduction, parameters that were identified as high priority for the seasonal process cruises in the SBI Phase II Implementation Plan. We will fully collaborate with, and make our data available to, other SBI investigators.

Sharon Smith (University of Miami, Rosenstiel School of Marine and Atmospheric Science)

Shelf-Basin Exchange of Large-Bodied Zooplankton [Copepods] in the Chukchi and Beaufort Seas

Physical forcing in the North Pacific/Western Arctic region exhibits abrupt regime shifts in which several decades (~25-35 years) of relatively cold, icy (2% above average) conditions are replaced in the span of a year or two by decades of warmer, less icy (3% below average) conditions; these cycles of climate in the region can be traced back at least to the late 1700s. The response of the Chukchi/Beaufort shelf ecosystem to warmer climate could follow two quite different pathways. In one scenario, warm periods would reduce ice cover and could create stronger thermal stratification, less mixing, limited nutrient supply, lower primary production, smaller-sized phytoplankton and smaller, coastal-like zooplankton. In a second scenario, also during warm periods with less ice, increased wind could result in shelf-break upwelling and mixing, enhanced nutrient supply, larger-sized phytoplankton and larger, deep-water zooplankton advected onto the shelf. Will global change, particularly warming, result in more large-sized zooplankton which support fish, birds, and mammals over the Chukchi and Beaufort shelves and slopes or smaller-sized zooplankton which will diminish the fish, birds, and mammals and favor sedentary benthic organisms?

Large-bodied copepods on the Chukchi and Beaufort shelves must be advected there from the slope waters of the Arctic Ocean or Bering Sea; none of them can complete their life cycles on the shelf itself. Therefore, they are tracers of shelf-basin exchanges. We seek to understand which large-bodied copepods reach the Chukchi (wide) and Beaufort (narrow) shelves, and the physical forcing (upwelling, intrusions, eddies) that might be responsible. Once on the shelves, how do size and reproductive responses of large copepods vary spatially, and what are the roles of physical processes and food supply? These responses define the robustness of the shelf habitat for supporting a pelagic ecosystem. Finally, we wish to determine which copepods are transported off the shelves and the physical processes (eddies, plumes) associated with that. Our investigation will: 1) define the distributions of the major taxa of zooplankton on the shelf, slope and in the open Arctic Ocean in summer, 2) measure copepod body and lipid sac sizes in different habitats, 3) measure female reproductive state, rates of egg production and egg hatching in different habitats, 4) describe the distribution of copepod nauplii and subadults in the region with the aid of molecular identification techniques, and 5) integrate these ecosystem measurements with the physical forcing (both observations and models) to understand how advection shapes the food web in the region.

James Swift (Scripps Institution of Oceanography), Lou Codispoti (University of Maryland/UMCES), Charles Flagg (Brookhaven National Laboratory), Terry Whitledge and Dean Stockwell (University of Alaska Fairbanks), Laurence Padman (ESRI), and Andreas Munchow (University of Delaware)

Collaborative Research: CTD/Hydrographic and Underway Service Measurements for the Shelf-Basin Interactions Phase II Field Project

The 3 year SBI Phase II field program will undertake ship operations in 2002-2004 using the USCGC Healy in 2002 and 2004 and USCG polar class vessels or equivalent, in 2003. This proposal address what National Science Foundation Solicitation 01-78 defines as service measurements on eight cruises during 2002-2005, and includes all service measurements defined in Solicitation 01-78, including CTD-based temperature, salinity, dissolved oxygen concentration, transmissivity, fluorescence and photosynthetically active radiation (PAR); rosette sample data to include inorganic nutrients (nitrate, nitrite, phosphate, silicate and ammonia), chlorophyll-a, salinity and dissolved oxygen concentrations; and underway measurements including (sea chest) temperature and salinity, standard meteorological observations, Acoustic Doppler Current Profiler (velocity and backscatter) on service measurement cruises from vessels which are equipped with ADCP, and various underway measurements made by SBI-designated science programs.

This is a collaborative proposal representing US scientific and technical service support groups from the UCSD Scripps Institution of Oceanography (Swift), Earth & Space Research (Padman), the University of Delaware (Muenchow), and University of Alaska, Fairbanks (Stockwell). Services from the University of Maryland Center for Environmental Science (Codispoti) and from Brookhaven National Laboratory (Flagg) are contained in subcontracts to the UCSD/SIO proposal. The UCSD Scripps Institution of Oceanography leads on the overall collaborative proposal and proposes to lead and coordinate the CTD/hydrographic and non-ADCP underway portion of the service measurements, with PI James H. Swift overall responsible for the service measurement program, except for the shipboard ADCP service measurements and Chl-a measurements. Shipboard technical support groups from the University of Alaska, Fairbanks (chemistry), the University of Maryland Center for Environmental Science (chemistry), the University of Washington (SeaBird CTD and chemistry), Oregon State University (chemistry), Texas A&M University (chemistry), and University of South Florida (chemistry) have indicated to Swift a strong interest in joint participation at sea, which Swift will handle via subcontracts from UCSD/SIO for specific personnel services on specific cruises to be determined after overall
consideration of the actual cruise schedules for SBI as well as for other US programs concurrent with SBI which may require high-quality routine chemistry. Earth & Space Research, Brookhaven National Laboratory, and the University of Delaware will be jointly responsible for underway shipboard ADCP service measurement. The University of Alaska, Fairbanks, is responsible for the Chl-a/pigment analyses. The University of Maryland Center for Environmental Science (Dr. Louis Codispoti) is working with Swift in the oversight of the sea program, data quality examination, and data reporting.

All service measurement participants are committed to support a data management plan that fully meets SBI and Solicitation 01-78 specifications. All reportable data resulting from the work proposed here will be available at sea to all SBI investigators in scientifically useful form and will be placed on-line at a site linked to the UCAR Joint Office for Science Support (JOSS) and/or delivered to JOSS (or other designated official data repository for the SBI Phase II Field Program) via express service shortly after the conclusion of each cruise. Data will be reported in preliminary, interim, and final form as appropriate, and with schedule, form, and format in accord with applicable NSF, ARCSS/OAII, and SBI Project guidelines and requirements.



Tom Weingartner (University of Alaska Fairbanks) and Knut Aagaard and Rebecca Woodgate (University of Washington)

Collaborative Research: The Fate of a Large and Strongly Forced Arctic Shelf Outflow: Physical and Biochemical Process Studies

Objectives:

1. To quantify the characteristics of the shelf outflow from the Chukchi Sea (e.g., transport, temperature, salinity), and to determine which upstream processes are principally responsible for the variability of these characteristics?

2. To quantify the variability of the system on seasonal and interannual timescales, and to assess what might be the connections with a changing climate?

3. To provide the temporal context of the Chukchi shelf water properties and flows useful to other SBI investigators who are addressing the regional biochemical and physical processes.

We will deploy four current meter moorings on the Chukchi continental shelf, with the moorings serviced annually during the mooring cruises. Each mooring will measure vertical profiles of horizontal velocity at hourly intervals using ADCPs. The moorings will also include 1 to 2 SeaCats or MicroCats, which will collect temperature, conductivity (for salinity), and in some cases pressure data. All instruments will sample at hourly intervals.

The mooring locations are:
a) 1 mooring in upper Barrow Canyon (~ 80 m isobath),
b) 1 mooring on the central shelf east of Herald Shoal (~ 50 m isobath),
c) 2 moorings on the outer Chukchi shelf east of the EEZ boundary one on the ~70 m isobath and the other on the ~100 m isobath.