Hydrodynamic response to cold fronts along the Louisiana coast

Cold fronts play important roles in flushing water out of the Louisiana estuaries. This study is aimed at examining the impact of cold front passages on the hydrodynamics in autumn-winter-spring of 2006-2007, and tries to determine the geographic difference, correlation and relative importance of winds, tides, and river discharge on water level variability and flow field. The amplitude spectra of water level reveal that diurnal tides dominate most stations. Areas west of 91°W have relatively high semidiurnal tides. The subtidal fluctuations are mainly wind-driven. Only the station in the Atchafalaya River shows obvious response to the spring flood of the Mississippi/Atchafalaya Rivers. Coastal bays have different water exchange rates depending on their water body area and geomorphology. Five largest flushing events correspond to migrating extratropical cyclones with frontal orientation perpendicular to the coastline, suggesting that wind direction is one of the controlling factors in the flushing rate and total transport. Both alongshore and cross-shore winds may effectively induce bay-shelf exchange. Northwest/north winds appear to be the most effective wind forcing in driving water movement from bay to shelf. Strong cold fronts may flush more than 40% of the bay waters onto the shelf within a period less than 40 hours. The near-surface current on the Louisiana inner shelf is mainly wind-driven, but tidal forcing becomes more important in the sub-surface layers or in the vicinity of the coastline of shallow waters. A prevailing down-coast flow occurs 81% and 70% of the time at CSI-6 and CSI-3, respectively. Strong cold front events may disturb this down-coast flow system by inducing a 1- to 3-day up-coast flow. At CSI-6, the Mississippi river discharge has little influence in non-flood seasons. During the period of spring flood, however, the large amount of freshwater exerts significant barotropic and baroclinic forcings on the current field and reinforces the down-coast flow. The analytical model reveals that the amplitudes of water level variations induced by alongshore and cross-shore wind forcings have the same order of magnitude (i.e., 10-1 m), indicating that they play almost equally important roles in driving the subtidal water level variability inside the bays

Early ice retreat and ocean warming may induce copepod biogeographic boundary shifts in the Arctic Ocean

Author Posting. © American Geophysical Union, 2016. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Oceans 121 (2016): 6137-6158, doi:10.1002/2016JC011784.Early ice retreat and ocean warming are changing various facets of the Arctic marine ecosystem, including the biogeographic distribution of marine organisms. Here an endemic copepod species, Calanus glacialis, was used as a model organism, to understand how and why Arctic marine environmental changes may induce biogeographic boundary shifts. A copepod individual-based model was coupled to an ice-ocean-ecosystem model to simulate temperature- and food-dependent copepod life history development. Numerical experiments were conducted for two contrasting years: a relatively cold and normal sea ice year (2001) and a well-known warm year with early ice retreat (2007). Model results agreed with commonly known biogeographic distributions of C. glacialis, which is a shelf/slope species and cannot colonize the vast majority of the central Arctic basins. Individuals along the northern boundaries of this species' distribution were most susceptible to reproduction timing and early food availability (released sea ice algae). In the Beaufort, Chukchi, East Siberian, and Laptev Seas where severe ocean warming and loss of sea ice occurred in summer 2007, relatively early ice retreat, elevated ocean temperature (about 1–2°C higher than 2001), increased phytoplankton food, and prolonged growth season created favorable conditions for C. glacialis development and caused a remarkable poleward expansion of its distribution. From a pan-Arctic perspective, despite the great heterogeneity in the temperature and food regimes, common biogeographic zones were identified from model simulations, thus allowing a better characterization of habitats and prediction of potential future biogeographic boundary shifts.National Science Foundation Polar Programs Grant Number: (PLR-1417677, PLR-1417339, and PLR-1416920)2017-02-2

Significance of beach geomorphology on fecal indicator bacteria levels

© The Author(s), 2017. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Marine Pollution Bulletin 121 (2017): 160-167, doi:10.1016/j.marpolbul.2017.05.024.Large databases of fecal indicator bacteria (FIB) measurements are available for coastal waters. With the assistance of satellite imagery, we illustrated the power of assessing data for many sites by evaluating beach features such as geomorphology, distance from rivers and canals, presence of piers and causeways, and degree of urbanization coupled with the enterococci FIB database for the state of Florida. We found that beach geomorphology was the primary characteristic associated with enterococci levels that exceeded regulatory guidelines. Beaches in close proximity to marshes or within bays had higher enterococci exceedances in comparison to open coast beaches. For open coast beaches, greater enterococci exceedances were associated with nearby rivers and higher levels of urbanization. Piers and causeways had a minimal contribution, as their effect was often overwhelmed by beach geomorphology. Results can be used to understand the potential causes of elevated enterococci levels and to promote public health.The early portion of this work was funded in part by the NSF–NIEHS Oceans and Human Health Program (NIEHS #P50 ES12736 and NSF #OCE0432368/0911373/1127813)

Biogeographic responses of the copepod Calanus glacialis to a changing Arctic marine environment

Author Posting. © The Author(s), 2017. This is the author's version of the work. It is posted here under a nonexclusive, irrevocable, paid-up, worldwide license granted to WHOI. It is made available for personal use, not for redistribution. The definitive version was published in Global Change Biology 24 (2018): e159-e170, doi:10.1111/gcb.13890.Dramatic changes have occurred in the Arctic Ocean over the past few decades, especially in terms of sea ice loss and ocean warming. Those environmental changes may modify the planktonic ecosystem with changes from lower to upper trophic levels. This study aimed to understand how the biogeographic distribution of a crucial endemic copepod species, Calanus glacialis, may respond to both abiotic (ocean temperature) and biotic (phytoplankton prey) drivers. A copepod individual-based model coupled to an ice-ocean-biogeochemical model was utilized to simulate temperature- and food-dependent life cycle development of C. glacialis annually from 1980 to 2014. Over the 35-year study period, the northern boundaries of modeled diapausing C. glacialis expanded poleward and the annual success rates of C. glacialis individuals attaining diapause in a circumpolar transition zone increased substantially. Those patterns could be explained by a lengthening growth season (during which time food is ample) and shortening critical development time (the period from the first feeding stage N3 to the diapausing stage C4). The biogeographic changes were further linked to large scale oceanic processes, particularly diminishing sea ice cover, upper ocean warming, and increasing and prolonging food availability, which could have potential consequences to the entire Arctic shelf/slope marine ecosystems.This study was funded by National Science Foundation Arctic System Science (ARCSS) Program (PLR-1417677, PLR-1417339, and PLR-1416920)

Wave energy level and geographic setting correlate with Florida beach water quality

Author Posting. © The Author(s), 2015. This is the author's version of the work. It is posted here for personal use, not for redistribution. The definitive version was published in Marine Pollution Bulletin 104 (2016): 54-60, doi:10.1016/j.marpolbul.2016.02.011.Many recreational beaches suffer from elevated levels of microorganisms, resulting in beach advisories and closures due to lack of compliance with Environmental Protection Agency guidelines. We conducted the first statewide beach water quality assessment by analyzing decadal records of fecal indicator bacteria (enterococci and fecal coliform) levels at 262 Florida beaches. The objectives were to depict synoptic patterns of beach water quality exceedance along the entire Florida shoreline and to evaluate their relationships with wave condition and geographic location. Percent exceedances based on enterococci and fecal coliform were negatively correlated with both long-term mean wave energy and beach slope. Also, Gulf of Mexico beaches exceeded the thresholds significantly more than Atlantic Ocean ones, perhaps partially due to the lower wave energy. A possible linkage between wave energy level and water quality is beach sand, a pervasive nonpoint source that tends to harbor more bacteria in the low-wave-energy environment.This work is funded by the NSF-NIEHS Oceans and Human Health Program (NIEHS # P50 ES12736 and NSF #OCE0432368/0911373/1127813)

Effect of IPA volume fraction on preferred orientation of zno nanowires grown by CBD method and mechanism

ZnO nanowires with semi-polar and non-polar orientations are fabricated on Si (100) substrates by low temperature chemical solution deposition. This distinctive growth is achieved by a co-effect of the seed layer templates and CBD solution. The growth mechanism is illustrated in detail and these semi-polar and non-polar ZnO/Si heterostructures show an excellent unidirectional conductivity