Instantaneous sediment accumulation rates in and around Tarr Inlet, Glacier Bay, Alaska.

Christina Biladeau

University of Washington School of Oceanography,

biladeau@u.washington.edu

Summary

            I hypothesize that instantaneous accumulation rates will decrease in Tarr Inlet as distance from the Grand Pacific and Marjorie glaciers increases. Instantaneous accumulation rates are unknown for Tarr Inlet and can provided as a basis for determining the burial rate of benthic biology, toxins and carbon. To test this hypothesis NetTraps (see Peterson et al. 2005) will be deployed at four stations in and southeast of Tarr Inlet to collect sediment. Deployment will occur aboard the R/V Thomas G. Thompson during 19-22 March, 2008. Onboard analysis will include determining accumulation rates and type of sediment collected using disceting- and microscopes. Other samples to be taken are small sediment samples from the top of shared sediment cores for comparison of seafloor and water column particle composition. The objectives of this study are 1) to determine the instantaneous accumulation rate in and around Tarr Inlet in late March, 2) to determine what is falling through the water column to be deposited as sediment and 3) to determine the burial rate of toxins in and around Tarr Inlet.

Introduction

            Collection of falling particles before they become sediment will reveal the type of particles that are available for sedimentation and will give a rate at which particles are accumulating. The transfer function method uses planktonic biota preserved in sediments as a proxy for past water temperature and conditions (Climap 1979). This method has been heavily scrutinized and comparison of composition of sinking particles to particles on the seafloor surface will indicate if sediment from within a core is a proper representation of the water column at the time of deposition (Crowley 2000). Sediment accumulation rates affect benthic biological communities. If rates are high the biology becomes stress and their density decreases (Moore and Scruton 1957). Accumulation rates also determine how fast toxins such as polycyclic aromatic hydrocarbons ( PAH’s) will be brought to the seafloor and the rate at which they are buried. PAH’s occur naturally in fossil fuels yet anthropogenic activities are  mainly responsible for PAH contamination (Curtosi et al. 2007). Glacier Bay is an Alaskan fjord with a high abundance of commercially valuable fish, as well as, top marine predators (Etherington et al. 2007). PAH contamination could cause extreme harm to this ecosystem. There is a critical need to understand the rate at which PAH’s are entering the water and leaving it through burial. In this study I intend to address the question of what is falling through the water column to become sediment.

Proposed Research

            In order to determine the instantaneous accumulation rate of sediment in and near Tarr Inlet, sediment will be collected using a NetTrap. The use of NetTraps will allow the examination of particles fluxing to the sediment, giving the opportunity to compare what is in the water column to what is deposited as sediment. NetTraps will be deployed at four stations in and southeast of Tarr Inlet (Fig. 1, Table 1). Deployment of NetTraps will take place on the R/V Thomas G. Thompson during 19-22 March, 2008. Sampling sites were chosen based on distance from the Grand Pacific and Marjorie glaciers. NetTraps will be deployed 20-48 hours depending on time availability for other projects aboard the R/V Thompson. The anchored traps will reside at 150 m depth with subsurface floats that will keep the net vertical. Seafloor sediment samples will also be taken at each station by other researchers, from these cores a small amount of sediment will be extracted for comparison to the particles from the traps.

Once the NetTraps are retrieved weight and volume of the collected sediment will be measured. Splitting of samples will be done using a zooplankton splitter, which will evenly distribute collected sediment into subsamples. Subsamples will be dried using both a centrifuge, to separate the water from the sediment, and a drying oven to burn off any excess water. Dry samples will be weighed and viewed under microscopes to determine sediment composition. Grain mounts will be made by placing small amounts of dry sediment in a petrologic proxy and letting it harden for 24 hours (pers. com. Kelley). All previously stated methods will take place aboard the R/V Thompson.

Post-cruise work includes making petrologic slides from the grain mounts at the University of Washington, as well as, examining the slides under a microscope. Results gained from Justin Bergquist’s ²¹⁰Pb analysis will be compared to my data to determine variability between instantaneous sediment accumulation rates and the year-long average. Data from Stephanie Keever’s PAH concentrations will also be compared with my data to determine the rate at which PAH’s are accumulating in Glacier Bay sediments.

            Time duration, order of shipboard and lab sampling is listed in Table 2. Special considerations for my research are the need for data from Bergquist and Keever, as stated before, during site sampling sediment cores must be done before net deployment or at least 2 km away and the NetTraps need to be in the water for a minimum of 20 hrs.

Budget

            Cost of ship time for R/V Thompson is $22,000/day, but will not be charged to student researchers. Applicable cost for this research is $576.00 (Table 3). No lab fees are being charged.

Table 1. Stations listed in order of priority.

Table 2. Time duration of shipboard sampling and lab time.

Table 3.

Figure 1. Map of stations in Glacier Bay.

References

CLIMAP Project. 1979. The surface of the Ice-Age Earth. Science. 191: 1131-1136

Crowley, T.J. 2000. CLIMAP SSTs re-revisited. Climate Dynamics. 16: 241-255

Curtosi, A. et al. 2007. Polycyclic aromatic hydrocarbons in soil and surface marine sediment       near Jubany Station (Antarctica). Role of permafrost as a low-permeability barrier. Sci   tot Envir. 383: 193-204

Etherington, L.L. et al. 2007. Oceanography of Glacier Bay, Alaska: Implications for biological    patterns in a glacial fjord estuary. Estuaries and Coasts. 30: 927-944

Kelley, D. 2008. Grain mount methods. Personal Communication.

Moore, P.G. 1977. Inorganic particle suspension in the sea and their effects on marine animals.     Oceanogr Mar Biol. 15: 224-363

Peterson, M.L. et al. Novel techniques of collection of sinking particles in the ocean and   determining their settling rates. Limnol. Oceanogr. 3: 520-532