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Yvette Spitz

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Papers by Yvette Spitz

The influence of sea ice and snow cover and nutrient availability on the formation of massive under-ice phytoplankton blooms in the Chukchi Sea

Deep Sea Research Part II: Topical Studies in Oceanography, 2015

A coupled biophysical model is used to examine the impact of changes in sea ice and snow cover an... more A coupled biophysical model is used to examine the impact of changes in sea ice and snow cover and nutrient availability on the formation of massive under-ice phytoplankton blooms (MUPBs) in the Chukchi Sea of the Arctic Ocean over the period 1988-2013. The model is able to reproduce the basic features of the ICESCAPE (Impacts of Climate on EcoSystems and Chemistry of the Arctic Pacific Environment) observed MUPB during July 2011. The simulated MUPBs occur every year during 1988-2013, mainly in between mid-June and mid-July. While the simulated under-ice blooms of moderate magnitude are widespread in the Chukchi Sea, MUPBs are less so. On average, the area fraction of MUPBs in the ice-covered areas of the Chukchi Sea during June and July is about 8%, which has been increasing at a rate of 2% yr-1 over 1988-2013. The simulated increase in the area fraction as well as primary productivity and chlorophyll a biomass is linked to an increase in light availability, in response to a decrease in sea ice and snow cover, and an increase in nutrient availability in the upper 100 m of the ocean, in conjunction with an intensification of ocean circulation. Simulated MUPBs are temporally sporadic and spatially patchy because of strong spatiotemporal variations of light and nutrient availability. However, as observed during ICESCAPE, there is a high likelihood that MUPBs may form at the shelf break, where the model simulates enhanced nutrient concentration that is seldom depleted between mid-June and mid-July because of generally robust shelf-break upwelling and other dynamic ocean processes. The occurrence of MUPBs at the shelf break is more frequent in the past decade than in the earlier period because of elevated light availability there. It may be even more frequent in the future if the sea ice and snow cover continues to decline such that light is more available at the shelf break to further boost the formation of MUPBs there.

The great 2012 Arctic Ocean summer cyclone enhanced biological productivity on the shelves

Journal of Geophysical Research: Oceans, 2014

A coupled biophysical model is used to examine the impact of the great Arctic cyclone of early Au... more A coupled biophysical model is used to examine the impact of the great Arctic cyclone of early August 2012 on the marine planktonic ecosystem in the Pacific sector of the Arctic Ocean (PSA). Model results indicate that the cyclone influences the marine planktonic ecosystem by enhancing productivity on the shelves of the Chukchi, East Siberian, and Laptev seas during the storm. Although the cyclone's passage in the PSA lasted only a few days, the simulated biological effects on the shelves last 1 month or longer. At some locations on the shelves, primary productivity (PP) increases by up to 90% and phytoplankton biomass by up to 40% in the wake of the cyclone. The increase in zooplankton biomass is up to 18% on 31 August and remains 10% on 15 September, more than 1 month after the storm. In the central PSA, however, model simulations indicate a decrease in PP and plankton biomass. The biological gain on the shelves and loss in the central PSA are linked to two factors. (1) The cyclone enhances mixing in the upper ocean, which increases nutrient availability in the surface waters of the shelves; enhanced mixing in the central PSA does not increase productivity because nutrients there are mostly depleted through summer draw down by the time of the cyclone's passage. (2) The cyclone also induces divergence, resulting from the cyclone's low-pressure system that drives cyclonic sea ice and upper ocean circulation, which transports more plankton biomass onto the shelves from the central PSA. The simulated biological gain on the shelves is greater than the loss in the central PSA, and therefore, the production on average over the entire PSA is increased by the cyclone. Because the gain on the shelves is offset by the loss in the central PSA, the average increase over the entire PSA is moderate and lasts only about 10 days. The generally positive impact of cyclones on the marine ecosystem in the Arctic, particularly on the shelves, is likely to grow with increasing summer cyclone activity if the Arctic continues to warm and the ice cover continues to shrink.

Modeling the impact of declining sea ice on the Arctic marine planktonic ecosystem

Journal of Geophysical Research: Oceans, 2010

We have developed a coupled 3-D pan-Arctic biology/sea ice/ocean model to investigate the impact ... more We have developed a coupled 3-D pan-Arctic biology/sea ice/ocean model to investigate the impact of declining Arctic sea ice on the marine planktonic ecosystem over 1988-2007. The biophysical model results agree with satellite observations of a generally downward trend in summer sea ice extent during 1988-2007, resulting in an increase in the simulated photosynthetically active radiation (PAR) at the ocean surface and marine primary productivity (PP) in the upper 100 m over open water areas of the Arctic Ocean. The simulated Arctic sea ice thickness has decreased steadily during 1988-2007, leading to an increase in PAR and PP in sea ice-covered areas. The simulated total PAR in all areas of the Arctic Ocean has increased by 43%, from 146 TW in 1988 to 209 TW in 2007; the corresponding total PP has increased by 50%, from 456 Tg C yr −1 in 1988 to 682 Tg C yr −1 in 2007. The simulated PAR and PP increases mainly occur in the seasonally and permanently ice-covered Arctic Ocean. In addition to increasing PAR, the decline in sea ice tends to increase the nutrient availability in the euphotic zone by enhancing air-sea momentum transfer, leading to strengthened upwelling and mixing in the water column and therefore increased nutrient input into the upper ocean layers from below. The increasing nutrient availability also contributes to the increase in the simulated PP, even though significant surface nutrient drawdown in summer is simulated. In conjunction with increasing surface absorption of solar radiation and rising surface air temperature, the increasing surface water temperature in the Arctic Ocean peripheral seas further contributes to the increase in PP. As PP has increased, so has the simulated biomass of phytoplankton and zooplankton.

Atmospheric Forcing, Sea-Ice Interannual Variability, and Ocean Current Impacts on the Availability of Bowhead Whale Prey Near Barrow, AK

The linkages between bowhead whale distributions, whale prey availability, ocean and ice processe... more The linkages between bowhead whale distributions, whale prey availability, ocean and ice processes, and atmospheric forcing and interannual environmental variability in the Northern Alaskan Coastal system near Barrow, AK are being explored through biological-physical modeling, field sampling, and retrospective analysis. Complimentary modeling approaches, based on the outputs of a pan-arctic ice-ocean model of 1/12° resolution and forced by realistic air-sea fluxes and wind stress, were employed to analyze the system response to several forcing scenarios typical of the last decade. The influence of extrinsic (Pacific) input of whale prey (euphausiids) to the region was explored. Euphausiids, an important prey of bowhead whales in the fall at Barrow, AK, must have been transported there from the Bering Sea since at present it is believed that they are not endemic. Transport experiments identified potential trajectories and transit times of euphausiids (whale prey) from Bering Strait to Barrow. For euphausiids seeded at the surface, the probability of reaching Barrow was only 1% in 1997 but 10% in 2002. Subsurface seeded euphausiids also traveled faster with the majority reaching Barrow one month earlier in 2002 than in 1997. These differences were due to stronger northward currents in 2002 than in 1997. Dye-tracer experiments identified the pathways and quantity of Pacific Water entering the Chukchi and Beaufort Seas as a proxy for biomass and nutrients. Results are discussed in the context of field observations. Future work will explore intrinsic mechanisms influencing whale prey abundance.

Effect of Local Winds on Salinity Intrusion in the Columbia River Estuary

Water

In the highly energetic Columbia River estuary, river discharge and tides are known as dominant f... more In the highly energetic Columbia River estuary, river discharge and tides are known as dominant factors controlling circulation. In this study, the 3D hydrodynamic unstructured-grid model SELFE is used to investigate the influence of the local wind on salinity intrusion. Numerical simulations are carried out for realistic conditions for the year 2014, with 4 km and 32 km resolution atmospheric forcing. The effect of the wind is further investigated by switching it off in the estuary. Analysis of modeled salinity intrusion length shows that the resolution of atmospheric forcing matters, and strong episodic winds occurring in winter and fall exert some control on this parameter. Energetic easterly winds tend to increase salinity intrusion length, while energetic westerly winds tend to do the reverse. Results also suggest that energetic winds can differentially alter salt intrusion in the two main channels—the north and south channels—of the estuary. These findings offer motivation for...

What drives Oregon shelf summer hypoxia?

Cornell University - arXiv, Jun 18, 2019

Using coupled biological-physical model based on NPZD-type biological model and 3D coastal ocean ... more Using coupled biological-physical model based on NPZD-type biological model and 3D coastal ocean model (ROMS) we studied dissolved oxygen (DO) dynamics and hypoxia development on Oregon shelf during April-August of 2002, 2006, and 2008. We found that shelf hypoxia existed during summer months of all three years. It was characterized by variable severity, horizontal and vertical extent, duration and timing, and it was more pronounced in 2002 and 2006. By the means of numerical sensitivity analysis we found out that: inadequate initial DO and NO3 conditions in late-spring 2002 prevented or delayed hypoxia development; offshore and especially northern DO and NO3 boundary conditions are important to simulating hypoxia on the Oregon shelf, this was especially critical for early bottom hypoxia on the shelf north of 45 o N in 2006; hypoxia occurred earlier in the north in 2006 and in the south (Heceta Bank) in 2002, perhaps, due to different northern boundary conditions for these years; the DO and NO3 conditions at western open boundary located some 400 km offshore are unimportant for DO dynamics in spring-summer. Although DO production due to biological processes is large, physical processes, mostly horizontal advection and diffusion, are responsible for net DO reduction in spring-summer and hypoxia onset in summer on the Oregon shelf. The physical mechanism most responsible for Oregon shelf hypoxia is the coastal upwelling. Diffusive fluxes of NO3 and DO are negligible at northern and southern boundaries of the Oregon shelf and appreciable at the western boundary. In 2006, about two thirds of total April-August DO loss happened in April-May as a result of strong and long-lasting upwelling event.

Using the 3D coupled physocal-biological model MIRO&CO-3D to assess diatom-Phaeocystis colony blooms in the Southern Bight of the North Sea and the response to short-term climatic and nutrient changes

ICES Workshop on Future Directions in Modelling Physical-Biological Interactions, Mar 7, 2004

info:eu-repo/semantics/publishe

Oregon Shelf Hypoxia Modeling

Modeling Coastal Hypoxia, 2017

Bottom hypoxia on the shelf in the Northeast Pacific is caused by different processes than coasta... more Bottom hypoxia on the shelf in the Northeast Pacific is caused by different processes than coastal hypoxia related to riverine inputs. Hypoxia off the coast of Oregon is a naturally occurring process as opposed to the anthropogenically forced hypoxia found in many coastal environments (e.g., Gulf of Mexico shelf, Chesapeake Bay). Off Oregon, bottom hypoxia occurs in summers that have large upwelling-driven near-bottom transport of high nitrate, low dissolved oxygen (DO) waters onto the shelf. The combination of low DO and high nitrate provides initially low (but not hypoxic) DO conditions near the bottom, and nitrate fertilization of shelf surface waters, leading to substantial phytoplankton production. Some production is grazed, and some of it sinks to the bottom where it decomposes consuming oxygen, creating bottom hypoxia in some years. Terrestrial runoff of nutrients into the system is small and not responsible for the development of bottom hypoxia. Similar processes contribute to natural hypoxia in other eastern boundary current upwelling regions, such as the Humboldt Current off Peru and the Benguela Current off Namibia and South Africa. We summarize the observational data on DO and illustrate the coupled biophysical modeling of hypoxia that has been done on the Oregon shelf. We compare hypoxia development in summer of 2002 and 2006, which differed in timing, spatial extent and intensity of hypoxia. Sensitivity analysis using various initial and boundary conditions for nitrate and dissolved oxygen reveals some of the essential conditions responsible for hypoxia development on the Oregon shelf.

A Feasibility Study of Dynamical Assimilation of Tide Gauge Data in the Chesapeake Bay

A FEA SIBILITY STUDY OF DYNAMICAL ASSIMILATION OF T ID E GAUGE DATA IN TH E CHESAPEAKE BAY Yvette... more A FEA SIBILITY STUDY OF DYNAMICAL ASSIMILATION OF T ID E GAUGE DATA IN TH E CHESAPEAKE BAY Yvette H uberte Spitz Old Dominion University, 1995 Director: Dr. J . M. Klinck The feasibility of dynam ical assimilation of surface elevation from tide gauges is investigated to estim ate the bottom drag coefficient and surface stress as a first step in improving modeled tidal and wind-driven circulation in the Chesapeake Bay. A two-dimensional shallow water model and an adjoint variational m ethod with a lim ited m em ory quasi-Newton optim ization algorithm are used to achieve this goal. Assimilation of tide gauge observations from ten perm anent stations in the Bay and use of a two-dimensional model adequately estim ate the bottom drag coefficient, wind stress and surface elevation at the Bay m outh. Subsequent use of these esti m ates in the circulation model considerably improves the modeled surface elevation in the entire Bay. Assimilation of predicted tidal elevations yields a drag c...

Modelling the seasonal behavior of two functional groups of phytoplankton in a Mediterranean Bay

Global Ecology and Oceanography of Harmful Algal Blooms (GEOHAB) Modelling Workshop Galway, Irela... more

Intraseasonal patterns in coastal plankton biomass off central Chile derived from satellite observations and a biochemical model

Journal of Marine Systems, 2017

Subseasonal (5-130 days) environmental variability can strongly affect plankton dynamics, but is ... more Subseasonal (5-130 days) environmental variability can strongly affect plankton dynamics, but is often overlooked in marine ecology studies. We documented the main subseasonal patterns of plankton biomass in the coastal upwelling system off central Chile, the southern part of the Humboldt System. Subseasonal variability was extracted from temporal patterns in satellite data of wind stress, sea surface temperature, and chlorophyll from the period 2003-2011, and from a realistically forced eddy-resolving physical-biochemical model from 2003 to 2008. Although most of the wind variability occurs at submonthly frequencies (b30 days), we found that the dominant subseasonal pattern of phytoplankton biomass is within the intraseasonal band (30-90 days). The strongest intraseasonal coupling between wind and plankton is in spring-summer, when increased solar radiation enhances the phytoplankton response to upwelling. Biochemical model outputs show intraseasonal shifts in plankton community structure, mainly associated with the large fluctuations in diatom biomass. Diatom biomass peaks near surface during strong upwelling, whereas small phytoplankton biomass peaks at subsurface depths during relaxation or downwelling periods. Strong intraseasonally forced changes in biomass and species composition could strongly impact trophodynamics connections in the ecosystem, including the recruitment of commercially important fish species such as common sardine and anchovy. The wind-driven variability of chlorophyll concentration was connected to mid-and high-latitude atmospheric anomalies, which resemble disturbances with frequencies similar to the tropical Madden-Julian Oscillation.

$Research paper thumbnail of Using the 3D Coupled Physical-Biological Model MIRO\ &CO-3D to Assess Diatom-Phaeocystis Colony Blooms in the Southern Bight of the North Sea and the Response to Short-Term Climatic and Nutrient Changes$

Using the 3D Coupled Physical-Biological Model MIRO\ &CO-3D to Assess Diatom-Phaeocystis Colony Blooms in the Southern Bight of the North Sea and the Response to Short-Term Climatic and Nutrient Changes

0info:eu-repo/semantics/publishe

Jet stream intraseasonal oscillations drive dominant ecosystem variations in Oregon's summertime coastal upwelling system

Proceedings of the National Academy of Sciences, 2007

Summertime wind stress along the coast of the northwestern United States typically exhibits intra... more Summertime wind stress along the coast of the northwestern United States typically exhibits intraseasonal oscillations (ISOs) with periods from ≈15 to 40 days, as well as fluctuations on the 2- to 6-day “weather-band” and 1-day diurnal time scales. Coastal upwelling of cool, nutrient-rich water is driven by extended periods of equatorward alongshore winds, and we show that the ≈20-day ISOs in alongshore wind stress dominated the upwelling process during summer 2001 off Oregon. These wind stress ISOs resulted from north–south positional ISOs of the atmospheric jet stream (JS). Upper-ocean temperature, phytoplankton, and zooplankton varied principally on the ≈20-day time scale as well, and these correlated with the ISOs in alongshore wind stress and JS position, even though there also were weather-band stress fluctuations of comparable magnitude. Such wind stress ISOs are typical along Oregon in the summer upwelling season, occurring in 10 of 12 years examined, including 2001. We pres...

Modeling Ocean Ecosystems: The PARADIGM Program

Oceanography, 2006

Modelling diatom and Phaeocystis blooms and nutrient cycles in the Southern Bight of the North Sea: the MIRO model

Marine Ecology Progress Series, 2005

The link between anthropogenic nutrient loads and the magnitude and extent of diatom and Phaeocys... more The link between anthropogenic nutrient loads and the magnitude and extent of diatom and Phaeocystis colony blooms in the Southern Bight of the North Sea was explored with the complex ecosystem model MIRO. The model was adapted for resolving the changing nutrient loads, the complex biology of the bloom species and the tight coupling between the benthic and pelagic compartments that characterise this shallow coastal shelf sea ecosystem. State variables included the main inorganic nutrients (nitrate [NO 3 ], ammonium [NH 4 ], phosphate [PO 4 ] and dissolved silica [DSi]), 3 groups of phytoplankton with different trophic fates (diatoms, nanophytoflagellates and Phaeocystis colonies), 2 zooplankton groups (copepods and microzooplankton), bacteria, and 5 classes of detrital organic matter with different biodegradability. The capability of the MIRO model to properly simulate the observed SW-NE gradient in nutrient enrichment and the seasonal cycle of inorganic and organic C and nutrients, phytoplankton, bacteria and zooplankton in the eastern English Channel and Southern Bight of the North Sea is demonstrated by running the model for the period from 1989 to 1999. The MIRO code was implemented in a simplified multi-box representation of the hydrodynamic regime. These model runs give the first general view of the seasonal dynamics of Phaeocystis colony blooms and nutrient cycling within the domain. C, N and P budget calculations show that (1) the coastal ecosystem has a low nutrient retention and elimination capacity, (2) trophic efficiency of the planktonic system is low, and (3) both are modulated by meteorological forcing.

Addition of inorganic or organic phosphorus enhances nitrogen and carbon fixation in the oligotrophic North Pacific

Marine Ecology Progress Series, 2011

We present a spatially extensive record of dinitrogen (N 2) fixation rates and distributions of N... more We present a spatially extensive record of dinitrogen (N 2) fixation rates and distributions of N 2 fixing microorganisms along with the results of exogenous phosphorus (P) addition experiments conducted during a series of cruises in the North Pacific Subtropical Gyre (NPSG). We measured the N 2 and carbon (C) fixation rates of natural plankton assemblages in response to the addition of methylphosphonate (MPn), a dissolved organic phosphorus (DOP) compound, and dissolved inorganic phosphorus (DIP). Results are compared to parallel unamended controls. These experiments produced 3 major findings: (1) MPn and DIP were utilized with equal metabolic efficiency over a single photoperiod, (2) the bulk of the enhanced N 2 fixation rates were within the range of those previously reported in the NPSG, suggesting that P levels in this region can be saturating but were not at the time of sampling and (3) MPn and DIP additions stimulated C fixation rates beyond estimated contributions by diazotrophs, and hence both DIP and bioavailable DOP additions could lead to enhancement of net primary productivity on short timescales. Our results suggest that the rate of N 2 fixation in our study region may have been restricted by the availability and/or the composition of the total P pool (inorganic and organic P) during our field season.

Data assimilation and a pelagic ecosystem model: parameterization using time series observations

Journal of Marine Systems, 1998

Variational adjoint assimilation of time series observations is used to estimate the optimal para... more Variational adjoint assimilation of time series observations is used to estimate the optimal parameters of a nitrogen-budget, Ž. upper ocean, mixed-layer ecosystem model. Observations collected at the Bermuda Atlantic Time-Series Study BATS site are taken as an example of a time series. A twin experiment using simulated data of the same type and frequency as the BATS observations first demonstrates the adequacy of the observations to estimate the model parameters and model the ecosystem annual cycle. This experiment further shows that some of the model parameters cannot be estimated independently. This conclusion leads to a simplification of the model and a redefinition of its parameters. Based upon the success of the twin experiment to estimate all model parameters, an attempt to assimilate actual observations from BATS was undertaken. The assimilation of real data leads to the conclusion that, even though the frequency and type of observations is adequate to estimate the model parameters, the considered model is not appropriate for the annual cycle of the BATS ecosystem.

The role of inorganic nutrients and dissolved organic phosphorus in the phytoplankton dynamics of a Mediterranean bay

Journal of Marine Systems, 2010

The effect of Dissolved Organic Phosphorus (DOP) availability and nutrient limitation of phytopla... more The effect of Dissolved Organic Phosphorus (DOP) availability and nutrient limitation of phytoplankton growth in an estuarine bay (Alfacs Bay, NW Mediterranean) have been studied by means of a zero-dimensional ecological model including nitrogen, phosphorus (organic and inorganic), two groups of phytoplankton (diatoms and flagellates), one group of zooplankton, and detritus. Simulations with and without DOP as an extra source of phosphorus for phytoplankton growth suggest that DOP plays an important role in the dynamics of the Alfacs Bay ecosystem. DOP is indeed necessary to simulate the observed draw-down of nitrate and build up of phytoplankton biomass. Two non-exclusive mechanisms allowing DOP availability for phytoplankton are possible: direct uptake, or remineralization to Dissolved Inorganic Phosphorus. Including both gives a better agreement with the observations. Inclusion of DOP in the model leads to predominance of phosphorus limitation of phytoplankton growth in fall and winter, and of nitrogen limitation in late spring and summer. Simulations with and without sediment resuspension suggest that this process does not significantly affect the nutrient budget in the bay.

Impacts of biological parameterization, initial conditions, and environmental forcing on parameter sensitivity and uncertainty in a marine ecosystem model for the Bering Sea

Journal of Marine Systems, 2011

We use a series of Monte Carlo experiments to explore simultaneously the sensitivity of the BEST ... more We use a series of Monte Carlo experiments to explore simultaneously the sensitivity of the BEST marine ecosystem model to environmental forcing, initial conditions, and biological parameterizations. Twenty model output variables were examined for sensitivity. The true sensitivity of biological and environmental parameters becomes apparent only when each parameter is allowed to vary within its realistic range. Many biological parameters were important only to their corresponding variable, but several biological parameters, e.g., microzooplankton grazing and small phytoplankton doubling rate, were consistently very important to several output variables. Assuming realistic biological and environmental variability, the standard deviation about simulated mean mesozooplankton biomass ranged from 1 to 14 mg C m − 3 during the year. Annual primary productivity was not strongly correlated with temperature but was positively correlated with initial nitrate and light. Secondary productivity was positively correlated with primary productivity and negatively correlated with spring bloom timing. Mesozooplankton productivity was not correlated with water temperature, but a shift towards a system in which smaller zooplankton undertake a greater proportion of the secondary production as the water temperature increases appears likely. This approach to incorporating environmental variability within a sensitivity analysis could be extended to any ecosystem model to gain confidence in climate-driven ecosystem predictions.

Modeling of ecosystem processes on the Oregon shelf during the 2001 summer upwelling

Journal of Geophysical Research, 2005

Three-dimensional ecosystem response to wind forcing on the continental shelf off Oregon is studi... more Three-dimensional ecosystem response to wind forcing on the continental shelf off Oregon is studied using a five-component nitrogen-based ecosystem model coupled to a high-resolution circulation model. We investigate, in particular, the influence of timedependent winds and alongshore variations in shelf topography for summer 2001 during the time period of the Coastal Ocean Advances in Shelf Transport (COAST) field experiment. Over summer 2001 the average southward, upwelling-favorable wind leads to the development of a southward coastal jet and upwelled cold nutrient-rich water over the shelf. A strong influence of the shelf topography is found in the observed and modeled nutrients and plankton, with significant spatial variability associated with interactions of the shelf flow with Heceta Bank. The model results show that the largest mean chlorophyll-a concentrations are located onshore of the coastal jet, while the largest mean zooplankton concentrations are found farther offshore, typically on the offshore side of the jet, except on Heceta Bank. During intermittent downwelling periods the largest concentrations of mean zooplankton and phytoplankton, however, are both inshore of the jet. The 20 day oscillations in the modeled nutrients and plankton, the time lags between the wind stress and these ecosystem components, and the decorrelation timescales of phytoplankton agree with those obtained from mooring and satellite measurements. A detailed analysis of the balance between biological and physical forcing helps to clarify the temporal and spatial response of the ecosystem.