Click on figures for larger images.

Figure 1.  Cut-away view showing an Anderson-type cone-shaped sediment trap, including the location of the Intervalometer, its attachment to the cross bar below the baffle, and the discharge of the partitions (discs) from the Intervalometer onto the surface of the sediment (Roger Anderson, University of New Mexico, written communication,  2008). The baffle at the top of the trap is installed to reduce turbulence at the opening and to reduce the volume of mega fauna entering the trap and possibly bioturbating the sediments in the collection tube.

Figure 2.  Photograph showing the deployment of Anderson-type sediment traps attached to a mooring wire during a Massachusetts Bay field experiment. The tube trap taped onto the wire was used for comparison purposes.

The Partition Intervalometer (see disclaimer) described in this manual is a state-of-the-art automated programmable timer that dispenses partitions (Teflon discs) at selected time intervals from a supply manifold into the collection tube of a sediment trap (fig. 1). The development, operation, testing procedures, and results from a field deployment of this instrumentation are described and illustrated in this manual.

Sediment traps are in situ devices routinely used to passively collect particulate material from the water column in a wide variety of coastal, oceanic, and limnological environments. The traps collect settling sediments, biological material, and aggregated particles and concentrate them into a collection tube. The trapped material may then be vertically extruded from the collection tube, sampled, and analyzed.

Determined by the Partition Intervalometer in conjunction with additional oceanographic instrumentation, the thickness and stratigraphy of the sediment layers provide insights regarding the flux and rates of sedimentation within the surrounding water column and on the sea floor; these rates are influenced by oceanic events such as storms, tidal cycles, or submarine landslides.

A variety of traps have been designed over the years, such as cones, cylinders, boxes, and more recently, automated traps that carry as many as 21 collection vials on a programmable motorized tray (U.S. Global Ocean Flux Study, 1989; McLane Research Laboratories, 2008).

Each trap design has inherent biases that affect the collection of suspended material under varying flow conditions and sampling environments. An example is how the geometry of a trap will yield a quantitative vertical flux across a horizontal plane (Hannan, 1984; Bothner, 1986; Butman, 1986).

Scientists from the U.S. Geological Survey (USGS) have an ongoing mandate to measure contaminant transport and to identify the ultimate depositional fate of suspended material in the marine environment. Accurate, delineated time-series samples collected from sediment traps are an important component for studying the flux and nature of suspended matter in the marine environment.

Researchers at the USGS Marine Science Centers in Woods Hole, Massachusetts, and Santa Cruz, California, typically use a baffled cone-shaped (20-degree cone angle) fiberglass Anderson type trap with an Intervalometer attached to a cross bar inside the sediment trap (Anderson, 1977). The sediment trap is vertically attached to an anchored subsurface mooring line with wire clamps in many of the Center’s marine, coastal, and deep-water field studies (fig. 2).