Katja Fennel

Katja Fennel
Dalhousie University | Dal · Department of Oceanography

PhD

About

181
Publications
39,534
Reads
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6,652
Citations
Additional affiliations
August 2006 - present
Dalhousie University
Position
  • Professor (Associate)
August 2002 - June 2006
Rutgers, The State University of New Jersey
Position
  • Professor (Assistant)
August 1999 - June 2002
Oregon State University
Position
  • PostDoc Position

Publications

Publications (181)
Article
Full-text available
Nutrient inputs from the Mississippi/Atchafalaya River system into the northern Gulf of Mexico promote high phytoplankton production and lead to high respiration rates. Respiration coupled with water column stratification results in seasonal summer hypoxia in bottom waters on the shelf. In addition to consuming oxygen, respiration produces carbon d...
Article
Full-text available
Rivers deliver large amounts of fresh water, nutrients, and other terrestrially derived materials to the coastal ocean. Where inputs accumulate on the shelf, harmful effects such as hypoxia and eutrophication can result. In contrast, where export to the open ocean is efficient riverine inputs contribute to global biogeochemical budgets. Assessing t...
Article
Aquatic environments experiencing low-oxygen conditions have been described as hypoxic, suboxic, or anoxic zones; oxygen minimum zones; and, in the popular media, the misnomer "dead zones." This review aims to elucidate important aspects underlying oxygen depletion in diverse coastal systems and provides a synthesis of general relationships between...
Article
Full-text available
The circulation in the northwestern North Atlantic Ocean is highly complex, characterized by the confluence of two major western boundary current systems and several shelf currents. Here we present the first comprehensive analysis of transport paths and timescales for the northwestern North Atlantic shelf, which is useful for estimating ventilation...
Article
Full-text available
The occurrence of hypoxia in coastal oceans is a long-standing and growing problem worldwide and is clearly linked to anthropogenic nutrient inputs. While the need for reducing anthropogenic nutrient loads is generally accepted, it is costly and thus requires scientifically sound nutrient-reduction strategies. Issues under debate include the relati...
Article
Full-text available
Measuring plankton and associated variables as part of ocean time-series stations has the potential to revolutionize our understanding of ocean biology and ecology and their ties to ocean biogeochemistry. It will open temporal scales (e.g., resolving diel cycles) not typically sampled as a function of depth. In this review we motivate the addition...
Article
Full-text available
Plain Language Summary The ocean is a major sink of anthropogenic CO2, but the magnitude, variability and regional differences of the uptake are not well understood or quantified. Continental shelves, in particular, are regions of intense and variable air‐sea exchange. Previous global studies reported that they follow a latitudinal trend where low‐...
Article
Full-text available
Continental shelves are thought to be affected disproportionately by climate change and are a large contributor to global air–sea carbon dioxide (CO2) fluxes. It is often reported that low-latitude shelves tend to act as net sources of CO2, whereas mid- and high-latitude shelves act as net sinks. Here, we combine a high-resolution regional model wi...
Article
Full-text available
The physical processes driving the genesis of surface- and subsurface-intensified cyclonic and anticyclonic eddies originating from the coastal current system of the Mauritanian Upwelling Region are investigated using a high-resolution (~1.5 km) configuration of GFDL’s Modular Ocean Model. Estimating an energy budget for the boundary current reveal...
Article
Full-text available
The marine nitrogen cycle is a main driver of ocean productivity and affects global climate. Despite decades of study, we still have an incomplete understanding of the role of the marine nitrogen cycle in the Earth system. While marine sediments play a major role in nitrogen cycling in the ocean, magnitudes and mechanisms are largely unconstrained....
Article
Full-text available
A reanalysis is a physically consistent set of optimally merged simulated model states and historical observational data, using data assimilation. High computational costs for modelled processes and assimilation algorithms has led to Earth system specific reanalysis products for the atmosphere, the ocean and the land separately. Recent developments...
Article
Coasts are those regions of the world where the land has an impact on the state of the sea, and that part of the land is in turn affected by the sea. This land–sea interaction may take various forms—geophysical, biological, chemical, sociocultural, and economic. Coasts are conditioned by specific regional conditions. These unique characteristics re...
Article
Full-text available
Given current threats to ocean ecosystem health, there is a growing demand for accurate biogeochemical hind-casts, nowcasts, and predictions. Provision of such products requires data assimilation, i.e., a comprehensive strategy for incorporating observations into biogeochemical models, but current data streams of biogeochemical observations are gen...
Article
Full-text available
Biogeochemistry has an important role to play in many environmental issues of current concern related to global change and air, water, and soil quality. However, reliable predictions and tangible implementation of solutions, offered by biogeochemistry, will need further integration of disciplines. Here, we refocus on how further developing and stre...
Preprint
Full-text available
Given current threats to ocean ecosystem health, there is a growing demand for accurate biogeochemical hindcasts, nowcasts, and predictions. Provision of such products requires data assimilation, i.e., a comprehensive strategy for incorporating observations into biogeochemical models, but current data streams of biogeochemical observations are gene...
Article
Full-text available
Continental shelf regions in the ocean play an important role in the global cycling of carbon and nutrients, but their responses to global change are understudied. Global Earth system models (ESMs), as essential tools for building understanding of ocean biogeochemistry, are used extensively and routinely for projections of future climate states; ho...
Preprint
Full-text available
Continental shelves are thought to be affected disproportionately by climate change and are a large contributor to global air-sea carbon dioxide (CO2) fluxes. It is often reported that low-latitude shelves tend to act as net sources of CO2 whereas mid- and high-latitude shelves act as net sinks. Here, we combine a high-resolution regional model wit...
Article
Full-text available
A three-dimensional physical-biological model of the marginal seas of China was used to analyze interannual and intra-seasonal variations in hypoxic conditions and identify the main processes controlling their generation off the Changjiang (or Yangtze River) estuary. The model was compared against available observations and reproduces the observed...
Preprint
Full-text available
Biogeochemistry has an important role to play in many environmental issues of current concern related to global change and air, water, and soil quality. However, reliable predictions and tangible take-up of solutions offered by biogeochemistry will need further integration of disciplines. Here, we emphasize how further developing ties between biolo...
Article
The need to characterize and track coastal hypoxia has led to the development of geostatistical models based on in situ observations of dissolved oxygen (DO) and mechanistic models based on a representation of biophysical processes. To integrate the benefits of these two distinct modeling approaches, we develop a space-time geostatistical framework...
Article
Full-text available
It is known that surface water eutrophication enhances bottom water ocean acidification via respiration in coastal oceans. However, the role of benthic processes in influencing bottom water acidification has not been sufficiently explored. We examined this issue by analyzing a 10‐year summer carbonate chemistry dataset in bottom water together with...
Article
Full-text available
Oceanic primary production forms the basis of the marine food web and provides a pathway for carbon sequestration. Despite its importance, spatial and temporal variations of primary production are poorly observed, in large part because the traditional measurement techniques are laborious and require the presence of a ship. More efficient methods ar...
Article
Full-text available
Biogeochemical ocean models are useful tools but subject to uncertainties arising from simplifications, inaccurate parameterization of processes, and poorly known model parameters. Parameter optimization is a standard method for addressing the latter but typically cannot constrain all biogeochemical parameters because of insufficient observations....
Preprint
Full-text available
Continental shelf regions in the ocean play an important role in the global cycling of carbon and nutrients but their responses to global change are understudied. Global Earth System Models (ESM), as essential tools for building understanding of ocean biogeochemistry, are used extensively and routinely for projections of future climate states; howe...
Article
Full-text available
Human activities have altered the state of the ocean, leading to warming, acidification and deoxygenation. These changes impact ocean biogeochemistry and influence ecosystem functions and ocean health. The long-term global effects of these changes are difficult to predict using current satellite sensing and traditional in situ observation technique...
Article
Full-text available
Human activities have altered the state of the ocean, leading to warming, acidification and deoxygenation. These changes impact ocean biogeochemistry and influence ecosystem functions and ocean health. The long- term global effects of these changes are difficult to predict using current satellite sensing and traditional in situ observation techniqu...
Article
Full-text available
In the East China Sea, hypoxia (oxygen ≤ 62.5 mmol m−3) is frequently observed off the Changjiang (or Yangtze River) estuary covering up to about 15 000 km2. The Changjiang is a major contributor to hypoxia formation because it discharges large amounts of freshwater and nutrients into the region. However, modeling and observational studies have sug...
Preprint
Full-text available
Abstract. Biogeochemical ocean models are useful tools subject to uncertainties arising from simplifications, inaccurate parameterization of processes, and poorly known model parameters. Parameter optimization is a standard method for addressing the latter but typically cannot constrain all biogeochemical parameters because of insufficient observat...
Preprint
Full-text available
Abstract. Oceanic primary production forms the basis of the marine food web and provides a pathway for carbon sequestration. Despite its importance, spatial and temporal variations of primary production are poorly observed, in large part because the traditional measurement techniques are laborious and require the presence of a ship. More efficient...
Article
Full-text available
Assessments of ocean data assimilation (DA) systems and observing system design experiments typically rely on identical or nonidentical twin experiments. The identical twin approach has been recognized as yielding biased impact assessments in atmospheric predictions, but these shortcomings are not sufficiently appreciated for oceanic DA application...
Article
The Mississippi-Atchafalaya River Basin delivers large amounts of fresh water and nutrients to the northern Gulf of Mexico promoting the development of a large hypoxic zone every summer. Statistical and semi-empirical models have long been used to provide seasonal forecasts of the mid-summer hypoxic extent using historic time series of spring nutri...
Article
Full-text available
A three-dimensional physical-biological model of marginal seas of China was used to analyze variations in hypoxic conditions and identify the main processes controlling their generation off the Changjiang Estuary. The model was validated against available observations and reproduces the observed temporal and spatial variability of hypoxia. Dissolve...
Article
Full-text available
In the East China Sea, hypoxia (oxygen ≤ 62.5 mmol m−3) is frequently observed off the Changjiang (or Yangtze) River estuary covering up to about 15,000 km². The Changjiang River is a major contributor to hypoxia formation because it discharges large amounts of freshwater and nutrients into the region. However, modelling and observational studies h...
Article
Full-text available
Assessments of ocean data assimilation (DA) systems and observing system design experiments typically rely on identical or fraternal twin experiments. The identical twin approach has been recognized as yielding biased impact assessments in atmospheric predictions but these shortcomings are not sufficiently appreciated for oceanic DA applications. H...
Article
Full-text available
The Argo Program has been implemented and sustained for almost two decades, as a global array of about 4000 profiling floats. Argo provides continuous observations of ocean temperature and salinity versus pressure, from the sea surface to 2000 dbar. The successful installation of the Argo array and its innovative data management system arose opport...
Article
Full-text available
The Argo Program has been implemented and sustained for almost two decades, as a global array of about 4000 profiling floats. Argo provides continuous observations of ocean temperature and salinity versus pressure, from the sea surface to 2000 dbar. The successful installation of the Argo array and its innovative data management system arose opport...
Article
Full-text available
The Mississippi and Atchafalaya River System discharges large amounts of freshwater and nutrients into the northern Gulf of Mexico (NGoM). These lead to increased stratification and elevate primary production in the outflow region. Consequently, hypoxia (oxygen <62.5 mmol/m³), extending over an area of roughly 15,000 km², forms every summer in bott...
Article
Objectively determining the level of ecosystem model complexity necessary to achieve meaningful representations of biogeochemical cycles at different spatial and temporal scales is an outstanding issue in marine ecosystem modeling.As part of the development of a three-dimensional (3D) Regional Ocean Modelling System (ROMS) application for the north...
Article
Full-text available
In this paper we review the technologies available to make globally quantitative observations of particles in general-and plankton in particular-in the world oceans, and for sizes varying from sub-microns to centimeters. Some of these technologies have been available for years while others have only recently emerged. Use of these technologies is cr...
Article
Full-text available
A quantification of carbon fluxes in the coastal ocean and across its boundaries with the atmosphere, land, and the open ocean is important for assessing the current state and projecting future trends in ocean carbon uptake and coastal ocean acidification, but this is currently a missing component of global carbon budgeting. This synthesis reviews...
Article
Full-text available
Ocean ecosystems are subject to a multitude of stressors, including changes in ocean physics and biogeochemistry, and direct anthropogenic influences. Implementation of protective and adaptive measures for ocean ecosystems requires a combination of ocean observations with analysis and prediction tools. These can guide assessments of the current sta...
Article
Full-text available
Predicting long-term impacts of introduced species is challenging, since stressors related to global change can influence species–community interactions by affecting both demographic rates of invasive species and the structure of the invaded ecosystems. Invasive species can alter ecosystem structure over time, further complicating interactions betw...
Article
Full-text available
Recent studies demonstrate that marine N2 fixation can be carried out without light by heterotrophic N2 fixers (diazotrophs). However, direct measurements of N2 fixation in aphotic environments are relatively scarce. Heterotrophic as well as unicellular and colonial photoautotrophic diazotrophs are present in the oligotrophic Gulf of Aqaba (norther...
Article
Full-text available
Coastal sediments adjacent to urban centers often receive high loads of organic matter (OM) due to large nutrient inputs from land that stimulate algae blooms. Early diagenetic models describing the remineralization of this OM in sediments have been developed for 50 years. Although these models can be applied to a range of marine sediments, specify...
Article
Full-text available
Resuspension affects water quality in coastal environments by entraining seabed organic matter into the water column, which can increase remineralization, alter seabed fluxes, decrease water clarity, and affect oxygen and nutrient dynamics. Nearly all numerical models of water column biogeochemistry, however, simplify seabed and bottom boundary lay...
Article
Full-text available
Global observations show that the ocean lost approximately 2% of its oxygen inventory over the past five decades1–3, with important implications for marine ecosystems4,5. The rate of change varies regionally, with northwest Atlantic coastal waters showing a long-term drop6,7 that vastly outpaces the global and North Atlantic basin mean deoxygenatio...
Article
Full-text available
The understanding of the seasonal variability of carbon cycling on the Scotian Shelf in the NW Atlantic Ocean has improved in recent years; however, very little information is available regarding its short-term variability. In order to shed light on this aspect of carbon cycling on the Scotian Shelf we investigate the effects of Hurricane Arthur, w...
Article
Full-text available
The continental shelf in the northern Gulf of Mexico experiences expansive seasonal hypoxic conditions and eutrophication-driven acidification in bottom waters. Rising surface ocean temperatures, freshwater and nutrient inputs, and atmospheric CO2 will further exacerbate these conditions. Using a high-resolution, regional circulation-biogeochemical...
Poster
Full-text available
We present a combined application of the Regional Ocean Modeling System (ROMS) and an element tracing technique to the northern Gulf of Mexico. We present results from a 10-year hindcast (2001-2011) and quantify the relative and absolute contributions of Mississippi and Atchafalaya nitrogen inputs to total nitrogen, net primary production and sedim...