AT42-15: Ohman "CCE-LTER3"

Ship

Cruise Party

Departure: Aug 5, 2019

Arrival: Sep 6, 2019

Operations Area

Science Objectives

Our objectives are to understand and quantify key mechanisms that transport coastal production and populations offshore in the CCE region, including the magnitudes and length scales of transport and their climate sensitivities.  The principal hypotheses we seek to test are:

H₁: Lateral transport dominated by the interaction of Ekman transport and westward propagating coastal filaments provides a significant flux of nutrients and organisms to offshore waters.

H₂: Carbon export associated with offshore transport is determined by in situ evolution of communities and nutrient regimes, and by subduction occurring largely at sharp frontal density gradients. 

The processes measured on this cruise will include primary and secondary production, net community production, carbonate system variables, grazing by microzooplankton and mesozooplankton, dissolved iron and ligand effects on phytoplankton growth, carbon and nitrogen cycling, and export of carbon and other elements in both particulate and dissolved forms.  The pelagic food web will be characterized, extending from viruses, prokaryotic and eukaryotic microbes, micro- and meso-zooplankton, to nektonic organisms (the latter as acoustic backscatter) using state-of-the-art measurement methods. 

Most measurements will be made in a Lagrangian reference frame while following discrete water parcels for 3-5 days at a time.  These water parcels will be selected to represent different stages in the temporal evolution of a coastal filament: i.e., nearshore near the upwelling source and presumed origin of the filament; somewhat further offshore, along the axis of the filament, as upwelled waters and entrained communities are advected offshore; and still further offshore, near the terminus of a filament, where export fluxes are expected to be elevated.  Our analyses will extend from the ocean surface through the euphotic zone, and in some locations into the mesopelagic ocean to 1000 m or deeper.  We also expect to conduct a brief Benthic Boundary Layer (BBL) study to understand the relationship between coastal iron supply in nearshore sediments and the flux of iron into the coastal ocean via coastal filaments. 

Our Broader Impacts activities will include seagoing research opportunities and training for multiple graduate students, undergraduate students and other volunteers, as well as regular communication with the general public via an online blog created by a graduate student. 

Science Activities

Our basic cruise design is Lagrangian, i.e., we will be following individual water parcels rather than sampling on a fixed grid of stations.  Each water parcel is selected based on real-time satellite imagery and in situ surveys (usually with a Moving Vessel Profiler).  Once an appropriate water parcel is identified, a satellite-tracked sediment trap array is released and used to follow the parcel and associated plankton populations for 3-5 days at a time while we make a series of other measurements.  Such measurements include CTD-rosette profiles, in situ imaging with an UVP5 plankton camera, seawater collections for in situ drifting incubations for growth and grazing experiments, shipboard deck incubations, Trace Metal CTD and Go-Flo casts for studies of iron limiation, zooplankton bongo net tows, MOCNESS vertically stratified net tows, live zooplankton collections for copepod egg production experiments, and other activities.

Vertical export of carbon and other elements will be determined by drifting sediment traps and a geochemical method that measures Th:Ur disequilibrium.

Continuous underway measurements will be made of O2:Ar ratios using a flow through mass spectrometer, CO2:pH using a custom carbonate system device, multi-spectral fluorescence using an Advanced Laser Fluorometer, multi-frequency acoustic backscatter using a Simrad (Kongsberg) EK-60, as well as standard flow-through measurements of T,S,O2, Chl-a fluorescence, Doppler currents, etc.   

A towed SeaSoar will be used to make larger-scale surveys of our study region toward the beginning and end of the cruise.  A free-fall Moving Vessel Profiler (MVP) with computer-controlled winch will conduct local site surveys and analyze small-scale spatial gradient repeatedly throughout the cruise.

Cross-frontal transects will be carried out that sample the gradient regions associated with coastal upwelling filaments, as well as the properties of the filament cores.

Supporting instruments will include a Spray glider deployed from shore as well as a new Zooglider deployed and recovered from Atlantis.

Additional Info

Stations:

Supporting documentation:

Shipboard Equipment

Shipboard Communication

CTD/Water Sampling

Critical CTD Sensors

MET Sensors

Sample Storage

Navigation

Navigation

Winches

Wire use and application

Standard Oceanographic Cables

Portable Vans

Checklist

Checklist