Summary

            Instantaneous accumulation rates are likely to 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 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 dissecting- 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late March, 2) to compare instantaneous accumulation rates to yearly averages in collaboration with J. Bergquist (2008 unpublished) 3) to determine the composition of the material falling through the water column to be deposited as sediment and 4) to determine the burial rate of toxins in and around Tarr Inlet in collaboration with S. Keever (2008 unpublished).

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 benthic biology become stressed 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 will be 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.    One method for determining accumulation rates is ²¹⁰Pb geochronology (Nittrouer et al. 1979). For this method, accumulation rate is assumed to be constant over time so that the vertical profile of ²¹⁰Pb can be used to calculate the accumulation rate (Dellapenna et al. 1998). However, Moore and Scruton (1957) determined that sediment deposited near the mouth of the Mississippi river, was deposited in regular and irregular layers. These differences were attributed to the fluctuation in amount of sediment being discharged into the system. These stochastic processes are expected in Glacier Bay, due to variable precipitation and the melting of marine and alpine glaciers. Instantaneous accumulation rates will be compared to average accumulation rates determined through ²¹⁰Pb geochronology done by J. Bergquist (2008 unpublished). This study intends to address the questions of what is falling through the water column to become sediment, at what rate accumulation is occurring in late March and how does this rate compare to the geological average.

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. The NetTraps being used  resembles a very large zooplankton net with a 1m diameter opening, 1m collar and 2m long conical walls constructed of 50-µm- mesh nylon net (Peterson et al. 2005). 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 evaporate 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 epoxy and letting it harden for 24 hours (pers. com. Kelley).

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 Bergquist ²¹⁰Pb analysis (2008 unpublished) will be compared to my data to determine variability between instantaneous sediment accumulation rates and the year-long average. Data from Keever’s PAH concentrations (2008 unpublished) 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. During site sampling sediment cores must be done before net deployment or at least 2 km away to reduce error from disturbed sediment 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. Proposed Budget

Figure 1. Map of stations in Glacier Bay (Hooge and Hooge 2002)

References

Bergquist, J. 2008. Sediment Accumulation rates in the West Arm of Glacier Bay, Alaska: based on ²¹⁰Pb analysis, geochronology and x-radiography. UW Ocean 444 unpublished.

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., E. Pelletier, C.L. Vodopivez and W.P. Mac. 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

Dellapenna, T.M., S.A. Kuehl and L.C. Schaffner. 1998. Sea-bed mixing and particle residence    times in biologically and physically daminated estuarine systems: a comparison of lower     Chesapeake Bay and the York River subestuary. Est. Coast Shelf Sci. 46: 777-795

Etherington, L.L., P.N. Hooge, E.R. Hooge and D.F. Hill. 2007. Oceanography of Glacier Bay,   Alaska: Implications for biological patterns in a glacial fjord estuary. Estuaries and             Coasts. 30: 927-944

Hooge, P. N., and E. R. Hooge. 2002. Fjord Oceanographic Processes in Glacier Bay, Alaska.

            148.