GLOBEC Primary Productivity and Mesoscale Variability
M. Abbott, R. Letelier [Oregon State University]
Project Summary
Recent studies in the California Current suggest that there are at least two types of ecological/physiological strategies. The nearshore community (dominated by large chain-forming and centric diatoms) may pursue a non-equilibrium strategy to exploit a physically-disrupted environment. For example, their ability to utilize light varies much more rapidly than their ability to harvest light, implying that they may respond rapidly to changes in physical forcing such as light and nutrient availability. The offshore community (dominated by small flagellates,) follows an equilibrium strategy with light harvesting and utilization nearly in balance. Our fundamental hypothesis is that the non-equilibrium community is more favorable for higher trophic levels such as euphausiids and hence juvenile salmon, and that spatial and temporal changes in the patterns of mesoscale variability will govern the extent of the non-equilibrium community. Our approach is to use rapid measurements of phytoplankton physiology in conjunction with detailed measurements of the physical environment.
Our plan is to track mesoscale features north and south of Cape Blanco, using bio-optical drifters, while making detailed fluorometric measurements. These will include Fast Repetition Rate Fluorometry (FRRF) and spectral measurements of downwelling irradiance and upwelling radiance, including sun-stimulated fluorescence. We will also compare these in situ observations with data from the next-generation ocean color sensor, MODIS, which will measure chlorophyll fluorescence efficiency. These measurements will focus on the following five basic questions:
Year 1 Tasks
The first year will focus on the first field surveys in the Cape Blanco area of the Oregon coast. These surveys will take place in mid-spring during the upwelling season and in late summer/early fall during the late stages of upwelling. The basic survey plan is described in the proposal by Cowles et al., but we provide a general outline here, focusing on our part. After the completion of the large-scale survey which will cover the entire study domain, there will be two small-scale surveys, one north and one south of Cape Blanco. During these surveys, we will collect underway measurements of photosynthetic parameters using a Chelsea Instruments Fast Repetition Rate Fluorometer (FRRF). Details on the types of parameters that can be measured are described below. The large-scale survey will provide the large-scale fields which will be compared with satellite imagery of chlorophyll fluorescence efficiency (CFE) which will be estimated by NASAâs Moderate Resolution Imaging Spectrometer (MODIS) which is part of the Earth Observing System (EOS). We will make similar underway measurements using the FRRF in the small-scale surveys, focusing primarily on identification of specific features for the Lagrangian study. At the conclusion of the first small-scale survey for each region, we will deploy 5 bio-optical drifters in a coherent array. We will follow this cluster for 24-36 hours, conducting detailed profiles of optical and fluorescence properties as well as collection of water samples for primary productivity measurements and pigment determinations. At the end of this period, the drifters will be recovered for subsequent deployments.
In addition to the field studies, we will rely on NASA support to process and analyze MODIS imagery for the entire GLOBEC study period. MODIS will launch on board Terra, the first EOS satellite, in July/August 1999. MODIS will measure chlorophyll concentrations as well as phytoplankton fluorescence. We expect that these data will complement SeaWiFS imagery which may be analyzed by other GLOBEC investigators (Strub).
Prior to the field work, we will acquire bio-optical drifters, probably
from METOCEAN Data Systems. We will make any necessary repairs
to the FRRF and the TSRB II. At the conclusion of the field work in Year
One, we will begin analysis of the observations in the context of the
science questions that we have posed.
This page was last updated on
March 14, 2007.
Maintained by:
Hal Batchelder
College of Oceanic and Atmospheric Sciences
Oregon State University
Corvallis, OR 97331-5503
phone: 541-737-4500; FAX 541-737-2064