Paul M. DiGiacomo

Satellite observations of small coastal ocean eddies in the Southern California Bight

This study describes the characteristics of extensive small-scale coastal ocean eddies in the Southern California Bight. These surface features were primarily detected by using ERS-1 and ERS-2 synthetic aperture radar (SAR) satellite imagery from 1992 to 1998. The eddies, predominantly cyclonic in their rotation, appeared to result from several forcing mechanisms. They were mainly observed within the Santa Barbara Channel and the Santa Monica-San Pedro Basin regions and appeared to be seasonal in their distribution. Observed eddy diameters were all less than 50 km, with over 70% less than 10 km. The SAR data were complemented by sea surface temperature measurements derived from advanced very high resolution radiometer satellite imagery, as well as in situ data from moorings and drifters that provided substantial verification of the small-scale eddies. These findings are significant in that the eddies were, in general, smaller in size and more abundant than previously reported. Additionally, these results provide further evidence of the complex near-surface circulation within the Southern California Bight, with important implications for nutrient flux, productivity, plankton patchiness, larval transport and recruitment, and dispersal of pollutants.

The United States' next generation of atmospheric composition and coastal ecosystem measurements : NASA's Geostationary Coastal and Air Pollution Events (GEO-CAPE) Mission

The Geostationary Coastal and Air Pollution Events (GEO-CAPE) mission was recommended by the National Research Councils (NRCs) Earth Science Decadal Survey to measure tropospheric trace gases and aerosols and coastal ocean phytoplankton, water quality, and biogeochemistry from geostationary orbit, providing continuous observations within the field of view. To fulfill the mandate and address the challenge put forth by the NRC, two GEO-CAPE Science Working Groups (SWGs), representing the atmospheric composition and ocean color disciplines, have developed realistic science objectives using input drawn from several community workshops. The GEO-CAPE mission will take advantage of this revolutionary advance in temporal frequency for both of these disciplines. Multiple observations per day are required to explore the physical, chemical, and dynamical processes that determine tropospheric composition and air quality over spatial scales ranging from urban to continental, and over temporal scales ranging from diu...

Phalaropes feeding at a coastal front in Santa Monica Bay, California

The spinning behavior often exhibited by phalaropes when feeding at freshwater sites is rarely observed at sea. Instead, phalaropes are typically observed slowly swimming forward while foraging on marine neuston concentrated in surface convergence zones. Small-scale coastal ocean fronts, eddies and internal waves capable of generating such convergences are extremely common, albeit ephemeral, features in the Southern California Bight. This region is marked by a complex flow regime, resultant in part from its variable coastal morphology. We used satellite data (AVHRR) and in situ measurements (CTD, surface drifters) to describe and track a coastal front in Santa Monica Bay, California, centrally located in the Southern California Bight. A high number of Red-necked Phalaropes (Phalaropus lobatus) were associated with this feature over the course of several days. Neuston tows and gut content analyses revealed these phalaropes were primarily feeding on fish eggs and assorted debris that were abundant at the sea surface in this front. No phalaropes were observed spinning anywhere in the vicinity. Previously unpublished metabolic activity rates for phalaropes indicate that spinning is much more energetically expensive than is swimming at a comparable speed. Convergences associated with fronts (or eddies, internal waves, etc.) in the Southern California Bight apparently provide phalaropes with a rich, easily accessible and steady supply of food without having to resort to the energetically costly behavior of spinning.

A model for partitioning the light absorption coefficient of natural waters into phytoplankton, nonalgal particulate, and colored dissolved organic components: A case study for the Chesapeake Bay

We present a model, referred to as Generalized Stacked-Constraints Model (GSCM), for partitioning the total light absorption coefficient of natural water (with pure-water contribution subtracted), anw(λ), into phytoplankton, aph(λ), nonalgal particulate, ad(λ), and CDOM, ag(λ), components. The formulation of the model is based on the so-called stacked-constraints approach, which utilizes a number of inequality constraints that must be satisfied simultaneously by the model outputs of component absorption coefficients. A major advancement is that GSCM provides a capability to separate the ad(λ) and ag(λ) coefficients from each other using only weakly restrictive assumptions about the component absorption coefficients. In contrast to the common assumption of exponential spectral shape of ad(λ) and ag(λ) in previous models, in our model these two coefficients are parameterized in terms of several distinct spectral shapes. These shapes are determined from field data collected in the Chesapeake Bay with an ultimate goal to adequately account for the actual variability in spectral shapes of ad(λ) and ag(λ) in the study area. Another advancement of this model lies in its capability to account for potentially nonnegligible magnitude of ad(λ) in the near-infrared spectral region. Evaluation of model performance demonstrates good agreement with measurements in the Chesapeake Bay. For example, the median ratio of the model-derived to measured ad(λ), ag(λ), and aph(λ) at 443 nm is 0.913, 1.064, and 1.056, respectively. Whereas our model in its present form can be a powerful tool for regional studies in the Chesapeake Bay, the overall approach is readily adaptable to other regions or bio-optical water types.

Opportunities and Challenges of Establishing Coastal Observing Systems

Some of the challenges to establishing and sustaining environmental monitoring are potentially overcome under the framework of global observing systems. Observing systems go beyond monitoring by enabling links between user needs and observations and by providing valued information products to user groups at appropriate spatial and temporal scales. The United Nations established three global observing systems; for climate, oceans, and land and freshwater. Initiatives have also begun to address important issues within coastal ecosystems. Recent socio-political awareness and technical advances have imporoved the opportunities for establishing these observing systems and ensuring their sustainability. Awareness and current technology alone are not enough, and ongoing implementation of these systems is still stymied by a variety of factors. We make several recommendations to promote their success now and in the future.

Enhancing the Global Ocean Observing System to meet evidence based needs for the ecosystem‐based management of coastal ecosystem services

Ecosystem-based approaches (EBAs) to managing anthropogenic pressures on ecosystems, adapting to changes in ecosystem states (indicators of ecosystem health), and mitigating the impacts of state changes on ecosystem services are needed for sustainable development. EBAs are informed by integrated ecosystem assessments (IEAs) that must be compiled and updated frequently for EBAs to be effective. Frequently updated IEAs depend on the sustained provision of data and information on pressures, state changes, and impacts of state changes on services. Nowhere is this truer than in the coastal zone, where people and ecosystem services are concentrated and where anthropogenic pressures converge. This study identifies the essential indicator variables required for the sustained provision of frequently updated IEAs, and offers an approach to establishing a global network of coastal observations within the framework of the Global Ocean Observing System. The need for and challenges of capacity-building are highlighted, and examples are given of current programmes that could contribute to the implementation of a coastal ocean observing system of systems on a global scale. This illustrates the need for new approaches to ocean governance that can achieve coordinated integration of existing programmes and technologies as a first step towards this goal.

Response to Comment on “Coastal Water Quality Impact of Stormwater Runoff from an Urban Watershed in Southern California”

Field studies were conducted to assess the coastal water quality impact of stormwater runoff from the Santa Ana River, which drains a large urban watershed located in southern California. Stormwater runoff from the river leads to very poor surf zone water quality, with fecal indicator bacteria concentrations exceeding California ocean bathing water standards by up to 500%. However, cross-shore currents (e.g., rip cells) dilute contaminated surf zone water with cleaner water from offshore, such that surf zone contamination is generally confined to < 5 km around the river outlet. Offshore of the surf zone, stormwater runoff ejected from the mouth of the river spreads out over a very large area, in some cases exceeding 100 km2 on the basis of satellite observations. Fecal indicator bacteria concentrations in these large stormwater plumes generally do not exceed California ocean bathing water standards, even in cases where offshore samples test positive for human pathogenic viruses (human adenoviruses and enteroviruses) and fecal indicator viruses (F+ coliphage). Multiple lines of evidence indicate that bacteria and viruses in the offshore stormwater plumes are either associated with relatively small particles (< 53 microm) or not particle-associated. Collectively, these results demonstrate that stormwater runoff from the Santa Ana River negatively impacts coastal water quality, both in the surf zone and offshore. However, the extent of this impact, and its human health significance, is influenced by numerous factors, including prevailing ocean currents, within-plume processing of particles and pathogens, and the timing, magnitude, and nature of runoff discharged from river outlets over the course of a storm.