Ecological Transitions in a Coastal Upwelling Ecosystem

The southern California Current Ecosystem (CCE) is a dynamic eastern boundary current ecosystem that is forced by ocean-atmosphere variability on interannual, multidecadal, and long-term secular time scales. Recent evidence suggests that apparent abrupt transitions in ecosystem conditions reflect linear tracking of the physical environment rather than oscillations between alternative preferred states. A space-for-time exchange is one approach that permits use of natural spatial variability in the CCE to develop a mechanistic understanding needed to project future temporal changes. The role of (sub)mesoscale frontal systems in altering rates of nutrient transport, primary and secondary production, export fluxes, and the rates of encounters between predators and prey is an issue central to this pelagic ecosystem and its future trajectory because the occurrence of such frontal features is increasing

Skill assessment via cross-validation and Monte Carlo simulation: an application to Georges Bank plankton models

Better methods are required to assess the skill or uncertainty of plankton model predictions. A method is presented which combines cross-validation with simulated repeat samplings of the data (Monte Carlo simulation), in order to robustly estimate uncertainty in predictions beyond the calibration data (‘extra-sample’). The method is applied to compare two bulk models of chlorophyll on Georges Bank using the GLOBEC data set, accounting for data and forcing errors as well as prior uncertainty in all model parameters and initial conditions. The first model is a simple interpolation of chlorophyll data (‘inductive’ model), and serves as a baseline of predictive skill. The second is a simple process model forced by interannually-variable nutrient and mesozooplankton mean fields. Uncertainty in the process model forcings severely increases the extra-sample prediction variance (over repeat experiments). Although the process model can reproduce some of the interannual chlorophyll variability via top-down control by mesozooplankton, other predictions are strongly biased, possibly due to neglected boundary fluxes of chlorophyll. As a result, the new skill metrics generally favour the inductive model. By contrast, a standard skill metric based on calibration data misfit incorrectly favours the process model, mainly due to the neglect of extra-sample prediction variance.<br/

The impact of Scotian Shelf Water cross-over on the plankton dynamics on Georges Bank: A 3-D experiment for the 1999 spring bloom

The 1999 March SeaWiFS images detected an intense phytoplankton bloom on the southern flank of Georges Bank (GB). The bloom covered a large portion of the southern flank between the 60 and 200 m isobaths, and later extended to and connected with an even larger patch near the Northeast Peak (NEP) and Browns Bank. A three-dimensional (3-D) model experiment was conducted to examine the cause of the bloom and the impact of Scotian Shelf Water on the spring phytoplankton bloom dynamics. The finite volume coastal ocean model (FVCOM) provided the hydrodynamic fields for Lagrangian particle trajectory, tracer and biological model experiments. Process-oriented modeling experiments showed that the formation and maintenance of the phytoplankton bloom on the southeastern flank of GB is related to the weak stratification caused by the transport of the colder but fresher Scotian Shelf Water across the Northeast Channel (NEC). With sufficient nutrients from the slope, the bloom could result from in situ growth of phytoplankton near the slope where the stabilizing salinity front is located. The model results suggest that the timing and location of the phytoplankton bloom on the southern flank of GB is sensitive to the spatial distribution of temperature and salinity on the bank, the flow fields across the NEC, and the location of the salinity front near the shelf break. © 2006 Elsevier Ltd. All rights reserved

Rapid phytoplankton response to wind forcing influences productivity in upwelling bays

Bays are often ecological hotspots within highly-productive eastern boundary upwelling systems. Though the physics of such bays are well understood, there is no consensus about the factors underlying their high productivity. Three weeks of high-temporal-resolution observations in two long, narrow bays (Rías Baixas, NW-Iberia), showed that during an upwelling pulse, deep, nutrient-rich isopycnals rose into the euphotic zone inside the rías in a few hours. The response of the isopycnals to changes in wind forcing is approximately three times faster inside the rías than the Ekman spin-up time, triggering rapid nutrient uptake and subsequent formation of a subsurface chlorophyll and production maximum. The tight coupling and rapid response of phytoplankton growth to wind forcing could explain the higher productivity of the rías, and also be at play in other upwelling bays with similar morphologies and orientations. Resolving short-term variability of physical–biological coupling is crucial to discern the future evolution of upwelling bays.</p

Spring phytoplankton bloom and associated lower trophic level food web dynamics on Georges Bank: 1-D and 2-D model studies

A coupled biological-physical model was developed and tested in one-dimensional (1-D, vertical) and two-dimensional (2-D, cross-sectional) domains to examine the spring phytoplankton bloom and associated lower trophic level food web dynamics on Georges Bank (GB). The biological model consists of nine compartments: dissolved inorganic nutrients (nitrate, ammonium and silicate), phytoplankton (large and small size classes), zooplankton (large and small size classes), and detrital organic nitrogen and biogenic silica. The 1-D model results showed that in the shallow central bank, the timing and duration of spring blooms are closely linked to the light intensity and its downward penetration, while the intensity of blooms is regulated by initial nutrient concentrations and zooplankton grazing pressure. In the deeper flank area, the bloom dynamics is directly controlled by the seasonal development of stratification. The interactions between the shallow and deep regions of the bank were examined by a 2-D model, which showed that the cross-sectional gradients of biological quantities were caused mainly by the shallow-deep topographic transition and tidal mixing. Between the shallow and deep regions, a possible phytoplankton maximum concentration area was seen in the model at the time before the formation of the tidal-mixing front. Once the tidal-mixing front was established during late spring, the model showed a relatively high concentration of phytoplankton near the front as the result of the tidally driven up-front nutrient flux. Both the 1-D and 2-D models captured the basic seasonal cycles of the nutrients and phytoplankton in the central bank, but failed to reproduce those patterns in the deep flank regions, where horizontal advection might play a significant role. © 2006 Elsevier Ltd. All rights reserved

Deepwater Horizon Oil Spill: A Review of the Planktonic Response

On April 20, 2010, the explosion of the Deepwater Horizon (DWH) oil rig resulted in the loss of 11 lives and the largest oil spill in US history (Graham et al., 2010) and perhaps the second largest in the world, after the first Gulf War Oil Spill from Kuwait. Over the 84 days following the explosion, an estimated 6.7 x 105 mT of Louisiana Sweet Crude oil (United States Government, 2011) and up to 500,000 mT of methane and gases (Joye et al., 2011) were released from 1,480 m below the ocean's surface into the Gulf of Mexico (GoM). As oil continued to escape from the seafloor throughout the summer of 2010, images of oiled wildlife pervaded the news. These pictures, though troubling, only hinted at the fate of the plankton that form the foundation of the GoM ecosystem. This review discusses the potential effects of the DWH oil spill on the overlooked, but extremely important, members of the GoM ecosystem—the plankton. Our assessment is based on data collected in the aftermath of the DWH spill and supplemented with studies from past oil spills when information on the GoM spill was limited or unavailable. The time line we develop traces the spill from a "planktonic perspective," emphasizing the population dynamics of marine bacteria, phytoplankton, zooplankton, and fish larvae

Journey to the Center of the Gyre: The Fate of the Tohoku Tsunami Debris Field

The 9.0 magnitude Tohoku earthquake that struck off the coast of Japan on March 11, 2011, was the fourth largest earthquake in recorded history and the largest ever to hit a densely populated region (Bertero, 2011; Lekkas et al., 2011). The ensuing tsunami inundated an area of about 561 km2 (Geospatial Information Authority, 2011), washing away an estimated 24.9 million tonnes of debris, including wood, sediments, plastics, industrial chemicals, and structural components (Oh, 2011). Two weeks following the tsunami, the meltdown of the Fukushima Daiichi nuclear reactors released radioactive elements into the atmosphere and coastal waters. Atmospheric deposition was found to be an important source of radioactivity in surface waters and may have contaminated the debris field, although the extent of this contamination remains unknown (Buesseler et al., 2012; Honda et al., 2012).Here, we follow the debris field along its predicted path from its source in Japanese coastal waters through the Kuroshio-Oyashio Extension, the North Pacific Current, and the California Current. From there, it will loop back toward the Hawaiian Islands, ultimately accumulating in the North Pacific Gyre (International Pacific Research Center, 2011b; Figure 1). Relying on precedents from previous natural disasters and ongoing observations, we attempt to predict the impact of this debris field on marine and coastal ecosystems in each of these regions. We predict that the Tohoku debris field will create a rare perturbation for ecosystems interconnected across the North Pacific, exacerbating the accumulating human impacts on the world ocean

Inhibition of growth rate and swimming speed of the harmful dinoflagellate Cochlodinium polykrikoides by diatoms: Implications for red tide formation

The harmful dinoflagellate Cochlodinium polykrikoides is responsible for red tides that cause large fish kills and extensive economic losses for the fishing industry. Diatoms, another component of planlctonic communities, may play critical roles in the red tide dynamics of C. polykrikoides. Possible inhibition of C polykrikoides growth rate and swimming speed by the common diatoms Chaetoceros danicus, Skeletonema costatum, and Thalassiosira decipiens through physical and chemical mechanisms was explored. S. costatum, C danicus, and T. decipiens reduced the swimming speed of C polykrikoides at diatom concentrations of &gt;5000, 25,000, and 1000 cells ml(-1), respectively. Filtrates from cultures of S. costatum, C. danicus, and T. decipiens also lowered swimming speeds of C polykrikoides, at diatom concentrations of &gt;250,000, 50,000, and 1000 cells ml(-1), respectively. S. costatum caused negative growth rates of C polykrikoides at concentrations of &gt;similar to 130,000 cells ml(-1), while C danicus caused negative growth rates at concentrations of &gt;similar to 1200 cells ml(-1). Simple models parameterized using the experimental data reproduced the changes in C polykrikoides cell concentrations driven by the presence of diatoms. Thus common diatoms may inhibit growth rate and swimming speed of C polykrikoides; reduce the depths reached by C polykrikoides through vertical migration; and, in turn, delay or prevent the outbreak of C polykrikoides red tides. (C) 2014 Elsevier B.V. All rights reserved.N