Spring bloom dynamics and zooplankton biomass response on the US Northeast Continental Shelf

This paper is not subject to U.S. copyright. The definitive version was published in Continental Shelf Research 102 (2015): 47-61, doi:10.1016/j.csr.2015.04.005.The spring phytoplankton bloom on the US Northeast Continental Shelf is a feature of the ecosystem production cycle that varies annually in timing, spatial extent, and magnitude. To quantify this variability, we analyzed remotely-sensed ocean color data at two spatial scales, one based on ecologically defined sub-units of the ecosystem (production units) and the other on a regular grid (0.5°). Five units were defined: Gulf of Maine East and West, Georges Bank, and Middle Atlantic Bight North and South. The units averaged 47×103 km2 in size. The initiation and termination of the spring bloom were determined using change-point analysis with constraints on what was identified as a bloom based on climatological bloom patterns. A discrete spring bloom was detected in most years over much of the western Gulf of Maine production unit. However, bloom frequency declined in the eastern Gulf of Maine and transitioned to frequencies as low as 50% along the southern flank of the Georges Bank production unit. Detectable spring blooms were episodic in the Middle Atlantic Bight production units. In the western Gulf of Maine, bloom duration was inversely related to bloom start day; thus, early blooms tended to be longer lasting and larger magnitude blooms. We view this as a phenological mismatch between bloom timing and the “top-down” grazing pressure that terminates a bloom. Estimates of secondary production were available from plankton surveys that provided spring indices of zooplankton biovolume. Winter chlorophyll biomass had little effect on spring zooplankton biovolume, whereas spring chlorophyll biomass had mixed effects on biovolume. There was evidence of a “bottom up” response seen on Georges Bank where spring zooplankton biovolume was positively correlated with the concentration of chlorophyll. However, in the western Gulf of Maine, biovolume was uncorrelated with chlorophyll concentration, but was positively correlated with bloom start and negatively correlated with magnitude. This observation is consistent with both a “top-down” mechanism of control of the bloom and a “bottom-up” effect of bloom timing on zooplankton grazing. Our inability to form a consistent model of these relationships across adjacent systems underscores the need for further research

Ocean and coastal acidification off New England and Nova Scotia

Author Posting. © The Oceanography Society, 2015. This article is posted here by permission of The Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 28, no. 2 (2015): 182-197, doi:10.5670/oceanog.2015.41.New England coastal and adjacent Nova Scotia shelf waters have a reduced buffering capacity because of significant freshwater input, making the region’s waters potentially more vulnerable to coastal acidification. Nutrient loading and heavy precipitation events further acidify the region’s poorly buffered coastal waters. Despite the apparent vulnerability of these waters, and fisheries’ and mariculture’s significant dependence on calcifying species, the community lacks the ability to confidently predict how the region’s ecosystems will respond to continued ocean and coastal acidification. Here, we discuss ocean and coastal acidification processes specific to New England coastal and Nova Scotia shelf waters and review current understanding of the biological consequences most relevant to the region. We also identify key research and monitoring needs to be addressed and highlight existing capacities that should be leveraged to advance a regional understanding of ocean and coastal acidification.This project was supported in part by an appointment to the Internship/Research Participation Program at the Office of Water, US Environmental Protection Agency (EPA), administered by the Oak Ridge Institute for Science and Education through an interagency agreement between the US Department of Energy and the EPA. JS acknowledges support from NASA grant from NNX14AL84G NASA-CCS

Nutrient Distributions in the Gulf of Maine: An Analysis of Spatial and Temporal Patterns of Dissolved Inorganic Nitrate and Silicate

While the Gulf of Maine has been historically well sampled relative to remote offshore regions, descriptions of the nutrient distributions and dynamics have provided only brief glimpses of restricted areas in space and time. The primary objectives of this study are to compile and evaluate the historical nutrient data within the region to determine the spatial and temporal variability of nutrient distributions, identify the environmental influences responsible for these patterns, and quantify the variability that exists within nutrient fluxes throughout the Gulf of Maine. Within five distinct regions in the Gulf of Maine, average seasonal cycles of dissolved inorganic nitrogen are similar, although there is regionally variable timing and magnitude of both nitrate and satellite measured chlorophyll biomass. A seasonal cycle of nitrate exists at all depths, however the variability is greater interannually than seasonally at depths greater than 50m. Seasonal surface anomalies can be explained by the timing of the spring phytoplankton bloom, correlated with salinity anomalies, and even related to zooplankton populations. All localized regions and depths within the Gulf of Maine are positively correlated, suggesting the entire Gulf typically varies as a cohesive unit. An objective analysis kriging interpolation generates a spatially explicit monthly climatology and identifies major features of the average nitrate concentrations in the water. This analysis also provides an objective measure of the historical sampling effort and indentifies locations and seasons lacking descriptive observations. A coupled nitrate-silicate box model for the Gulf of Maine shows that while nitrate is influenced heavily by offshore inputs, silicate has a dominant continental source. The historical data suggest biologically available nutrient fluxes can vary by as much as 50% annually and are highly dependent on outflows of Maine Intermediate Water. While the variability in nutrient concentrations is not the only factor determining biological productivity, these results show the possible influence of nutrient variability from a bottom-up trophic perspective within the Gulf of Maine