Ls Models Ls Island Issue 03 Midsummer
Sacha Weakland
A few months later, I found myself in the Bering Sea and north Pacific Ocean as a marine fisheries observer working on boats out of Dutch Harbor, AK. After you spend some time at sea peering into the water day and night, you start to see new things. I began to take note of these tiny little specks in the water that sparkled in the sunlight and sometimes even in the moonlight. This generated some interesting questions. What were the sparkles (phytoplankton reflecting sunlight and bioluminescence during night), What controls their abundance? (growth and mortality), In turn, what controls their growth and mortality? (nutrients, sunlight, temperature, grazers), What happens when phytoplankton are provided high concentrations of nitrogen and phosphorus? (blooms, eutrophication, hypoxia, and coastal acidification)? After several years at sea pondering these things, I decided I needed go to graduate school to learn how to find the answers.
This led me to the University of Alabama and the Dauphin Island Sea Lab where my PhD research focused on biogeochemical processes affecting nitrogen and phosphorus concentrations and eutrophication responses in estuaries and the coastal ocean. After graduating, I joined the U.S. Environmental Protection Agency as a post-doc and eventually was hired into a permanent position where I worked for thirteen years as research ecologist on water quality issues related to nutrient pollution and eutrophication. During this period, I learned new research methods in numerical ecosystem modeling and satellite ocean color applications to better understand drivers of estuarine and coastal water quality. In 2016, I was offered a position at the University of South Alabama and Dauphin Island Sea Lab. Having many fond memories of the Sea Lab from my graduate school days and with the lure of having a lab located at the tip of a barrier island where one may stand in one spot and look north to Mobile Bay and turn around and look south into the vast, blue Gulf of Mexico, I jumped at this opportunity. I am now a Professor and the Associate Director of the new School of Marine and Environmental Sciences at the University of South Alabama and a Senior Marine Scientist at the Sea Lab.
Our lab seeks to understand and quantify the processes controlling eutrophication, hypoxia, andthe biogeochemical cycling of carbon, oxygen, and nutrients in coastal ecosystems and howthese processes are related to anthropogenic drivers occurring at local, regional, and globalscales.
Our field and lab studies are directed at understanding the biogeochemical cycles of carbon, oxygen, nitrogen, and phosphorus in coastal systems and how these cycles are impacted by anthropogenic change such as watershed land-use change, increasing nutrient pollution, and climate change.Often, though, it is not possible to isolate how individual or cumulative environmental pressures affects an ecosystem through observation alone. In such cases, we build and employ numerical ecosystem models to tease apart multiple mechanisms that cannot be observed independently in large marine ecosystems.Ecosystem models are also useful for data synthesis and identification of knowledge gaps in our understanding of specific processes, which can lead to new hypotheses about how marine systems are organized and operate.We have developed and applied models ranging from coastal watershed hydrologic and nutrient exports models to coastal three-dimensional hydrodynamic, biogeochemical, and lower trophic level food web models to understand and predict how local and global anthropogenic perturbations impact expressions of coastal eutrophication such as phytoplankton blooms, hypoxia, coastal acidification, and declining water clarity.
Map of sampling locations in Perdido Bay, Mobile Bay, Mobile River Delta, and Mississippi Sound. Black squares are stations where only water is sampled. Red stations are where both water and sediments are sampled. Field observations are used to quantify biogeochemical cycling rates and long-term patterns and trends. Observations are also used as calibration and validation data for numerical models and satellite ocean color algorithms.
Ocean color satellites provide global, spatially synoptic, coastal data on a daily frequency for many water quality variables such as phytoplankton biomass (chlorophyll a), dissolved and particulate organic carbon, suspended sediments, and water clarity. Some satellites such as MODIS have been collecting data for nearly 20 years and provide excellent time-series of data that may be analyzed in relation to environmental trends and variability to better understand the drivers of changing water quality.
Estuaries and coastal ecosystems are located at the land-sea interface and are among the most highly productive systems on Earth. Due to their proximity to land and high human population centers, these ecosystems are also among the most susceptible to human activities. We focus on the impacts of land-use change, nutrient pollution, eutrophication, and hypoxia as multiple stressors impacting living resources. A central question is: How do these stressors along with a myriad of other stressors such as, ocean acidification, increasing sea surface temperatures, alterations in watershed hydrology, and harvesting of natural resources combine to impact water and habitat quality and the supported flora and fauna. Our research aims to disentangle and quantify how these stressors manifest both individually and cumulatively in coastal systems, and to predict how the systems may change following management or restoration activities. We use lab, field, and models to do this. Notably, the Dauphin Island Sea Lab just built a state-of-the-art multiple stressor laboratory that allows for simultaneous manipulation of temperature, salinity, oxygen, and pH to examine multiple stressors impacts on fauna and flora in independent experimental tanks. We use our field and ecosystem modeling studies to inform the combinations, levels, and frequencies of stressors that may be encountered in different parts of the coastal seascape and are now applying these stressor levels to oysters, blue crab, and spotted seatrout in the new laboratory. Our goal is to identify and understand water quality thresholds needed to sustain coastal shellfish and finfish populations.
John Lehrter, Ph.D., 2002, University of Alabama
Professor of Marine Sciences, University of South Alabama
Associate Director, School of Marine and Environmental Science, University of South Alabama
Senior Marine Scientist III at Dauphin Island Sea Lab
Freshwater stress. At least 18 million people live on islands too small for the current generation of global climate models (GCMs) to resolve. A study recently published in Nature Climate Change circumvents this problem to provide projections of future freshwater stress on 80 small island nations and groups.
"No challenge poses a greater threat to future generations than climate change," said President Barack Obama in his State of the Union address on January 20, 2015. Climate change is a global problem, but the impacts are felt locally. "...rising oceans, longer, hotter heat waves, dangerous droughts and floods, and massive disruptions that can trigger greater migration and conflict and hunger around the globe. The Pentagon says that climate change poses immediate risks to our national security. We should act like it." The Oceans and Climate Lab at CU Boulder combines "big data" (dozens of global climate models, satellites, etc.) as well as pinpoint measurements to understand the impacts of climate variability and change on marine ecosystems, transportation, freshwater resources, sea level, and tropical cyclones.
A downscaling approach is applied to future projection simulations from four CMIP5 global climate models to investigate the response of the tropical cyclone (TC) climatology over the North Pacific basin to global warming. Under the influence of the anthropogenic rise in greenhouse gases, TC-track density, power dissipation, and TC genesis exhibit robust increasing trends over the North Pacific, especially over the central subtropical Pacific region. The increase in North Pacific TCs is primarily manifested as increases in the intense and relatively weak TCs. Examination of storm duration also reveals that TCs over the North Pacific have longer lifetimes under global warming.
Through a genesis potential index, the mechanistic contributions of various physical climate factors to the simulated change in TC genesis are explored. More frequent TC genesis under global warming is mostly attributable to the smaller vertical wind shear and greater potential intensity (primarily due to higher sea surface temperature). In contrast, the effect of the saturation deficit of the free troposphere tends to suppress TC genesis, and the change in large-scale vorticity plays a negligible role.
Seasonal hurricane activity is a function of the amount of initial disturbances (e.g., easterly waves) and the background environment in which they develop into tropical storms (i.e., the main development region). Focusing on the former, a set of indices based solely upon the meridional structure of satellite-derived outgoing longwave radiation (OLR) over the African continent are shown to be capable of predicting Atlantic seasonal hurricane activity with very high rates of success. Predictions of named storms based on the July OLR field and trained only on the time period prior to the year being predicted yield a success rate of 87%, compared to the success rate of NOAA's August outlooks of 53% over the same period and with the same average uncertainty range (2). The resulting OLR indices are statistically robust, highly detectable, physically linked to the predictand, and may account for longer-term observed trends.
The airline industry closely monitors the midlatitude jet stream for short-term planning of flight paths and arrival times. In addition to passenger safety and on-time metrics, this is due to the acute sensitivity of airline profits to fuel cost. US carriers spent US$47 billion on jet fuel in 2011, compared with a total industry operating revenue of US$192 billion. Beyond the timescale of synoptic weather, the El Nio/Southern Oscillation (ENSO), Arctic Oscillation (AO) and other modes of variability modulate the strength and position of the Aleutian low and Pacific high on interannual timescales, which influence the tendency of the exit region of the midlatitude Pacific jet stream to extend, retract and meander poleward and equatorward1, 2, 3. The impact of global aviation on climate change has been studied for decades owing to the radiative forcing of emitted greenhouse gases, contrails and other effects4, 5. The impact of climate variability on air travel, however, has only recently come into focus, primarily in terms of turbulence6, 7. Shifting attention to flight durations, here we show that 88% of the interannual variance in domestic flight times between Hawaii and the continental US is explained by a linear combination of ENSO and the AO. Further, we extend our analysis to CMIP5 model projections to explore potential feedbacks between anthropogenic climate change and air travel.
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