Wind-driven modification of the Alaskan coastal current

Author Posting. © American Geophysical Union, 2012. 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 117 (2012): C03031, doi:10.1029/2011JC007650.Across-shelf transects over the eastern flank of Barrow Canyon were obtained in August 2005 with an autonomous underwater vehicle (AUV). Here, the shelf topography creates a “choke” point in which a substantial portion of Pacific inflow from the Bering Strait is concentrated within 30 km of the coast, providing an ideal setup for monitoring the flow with the AUV. Four transects, extending ∼10 km offshore of Barrow, Alaska, inshore of the ∼80 m isobath, were used in conjunction with a process-oriented numerical model to diagnose the wind-driven modification of the Alaskan coastal current. Poleward transports of 0.12 Sv were consistent among all sections, although the transport-weighted temperature was about 1°C colder in the transect obtained during peak winds. An idealized numerical model reproduces the observed hydrographic structure and across-shelf circulation reasonably well in that (1) winds were not sufficient to reverse the poleward flow, (2) upwelling was most pronounced in the nearshore, and (3) the onshore return flow occurred throughout the interior as opposed to the bottom boundary layer. The across-shelf circulation provides a possible mechanism for a meltwater intrusion observed on the offshore side of the AUV transect made during peak winds. Also of interest is that the observed anticyclonic shear was much stronger (∣∂u/∂y∣ > f) than previously measured in the region.Field work and analysis (A.J.P.) was supported by the Comer Science Education Foundation and the WHOI Ocean and Climate Change Institute. E.L.S. was supported as a WHOI Postdoctoral Scholar.2012-09-2

Nonlinear internal waves on the continental shelf

The properties and evolution of nonlinear internal waves (NLIWs) depend upon the background conditions within which waves form, propagate, and dissipate. As a result, the NLIW field on the New Jersey shelf displayed dramatic variability during the Shallow Water 2006 experiment. Wave variability was exhibited by 1) amplitudes that ranged from 5 m to over 20 m, 2) irregular wave arrival times, and 3) wave forms that were either mode-1 or mode-2 in vertical structure. Over the month-long experiment, a six-day time span, which was coincident with the neap tide, was distinguished by having the largest observed NLIWs. The change in character of the observed waves between this period and the remainder of the month resulted in wave energies that increased by a factor of 5-10. The wave energy budget also varied spatially, as waves propagated across the shelf. On the outer shelf, energy was supplied to the NLIWs by the internal tide; and, inshore the balance shifted so that the change in energy per unit time was balanced by dissipative loss in the waves. While at a particular location dissipation in the core of the waves had only a weak dependence on energy, the average dissipative loss scaled with the maximum energy of the waves. NLIW dissipation was dominated by shear-driven turbulence in the mixed layer; at the pycnocline depth, NLIW dissipation was on average 10 times larger than that observed in background profiles. Consequently, the passage of NLIWs resulted in large heat fluxes across the pycnocline, contributing as much as 50% to the total average heat flux on the shelf. These changes in energetics were accompanied by structural changes in the wave form, including changes induced by wave interactions and the polarity reversal of three large-amplitude wave groups

An Intrathermocline Eddy and a tropical cyclone in the Bay of Bengal

The Bay of Bengal, subjected to monsoonal forcing and tropical cyclones, displays a complex field of ocean eddies. On 5 December 2013 a sub-surface vortex or Intrathermocline Eddy (ITE) composed of water characteristic of the Andaman Sea was observed within the thermocline of the western Bay of Bengal. We propose that the ITE was the product of Tropical Cyclone Lehar interaction on 27 November 2013 with a westward propagating surface eddy from the eastern Bay of Bengal. While Lehar’s interaction with the ocean initially removes heat from the upper layers of the eddy, air-sea flux is limited as the deeper portions of the eddy was subducted into the stratified thermocline, inhibiting further interaction with the atmosphere. The ITE core from 30 to 150m is thus isolated from local air-sea fluxes by strong stratification at the mixed layer base, and its periphery is stable to shear instability, suggestive of longevity and the ability to carry water far distances with minimal modification

Bay of Bengal : 2013 northeast monsoon upper-ocean circulation

Author Posting. © The Oceanography Society, 2016. This article is posted here by permission of The Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 29, no. 2 (2016): 82–91, doi:10.5670/oceanog.2016.41.The upper 200 m of the two northern Indian Ocean embayments, the Bay of Bengal (BoB) and the Arabian Sea (AS), differ sharply in their salinity stratification, as the Asian monsoon injects massive amounts of freshwater into the BoB while removing freshwater via evaporation from the AS. The ocean circulation transfers salt from the AS to the BoB and exports freshwater from the BoB to mitigate the salinity difference and reach a quasi-steady state, albeit with strong seasonality. An energetic field of mesoscale features and an intrathermocline eddy was observed within the BoB during the R/V Revelle November and December 2013 Air-Sea Interactions Regional Initiative cruises, marking the early northeast monsoon phase. Mesoscale features, which display a surprisingly large thermohaline range within their confines, obscure the regional surface water and thermohaline stratification patterns, as observed by satellite and Argo profilers. Ocean processes blend the fresh and salty features along and across density surfaces, influencing sea surface temperature and air-sea flux. Comparing the Revelle observations to the Argo data reveals a general westward migration of mesoscale features across the BoB.Support for Bay of Bengal research is provided by the Office of Naval Research. ALG award number N00014-14-10065. AM and MF award number N00014-13-10451 and for MF a WHOI summer student fellowship. ES award number N00014-14-10236

Seasonal control of Petermann Gletscher ice-shelf melt by the ocean's response to sea-ice cover in Nares Strait

Petermann Gletscher drains ~4% of the Greenland ice sheet (GrIS) area, with ~80% of its mass loss occurring by basal melting of its ice shelf. We use a high-resolution coupled ocean and sea-ice model with a thermodynamic glacial ice shelf to diagnose ocean-controlled seasonality in basal melting of the Petermann ice shelf. Basal melt rates increase by ~20% in summer due to a seasonal shift in ocean circulation within Nares Strait that is associated with the transition from landfast sea ice to mobile sea ice. Under landfast ice, cold near-surface waters are maintained on the eastern side of the strait and within Petermann Fjord, reducing basal melt and insulating the ice shelf. Under mobile sea ice, warm waters are upwelled on the eastern side of the strait and, mediated by local instabilities and eddies, enter Petermann Fjord, enhancing basal melt down to depths of 200 m. The transition between these states occurs rapidly, and seasonal changes within Nares Strait are conveyed into the fjord within the same season. These results suggest that long-term changes in the length of the landfast sea-ice season will substantially alter the structure of Petermann ice shelf and its contribution to GrIS mass loss

Freshwater in the Bay of Bengal : its fate and role in air-sea heat exchange

Author Posting. © The Oceanography Society, 2016. This article is posted here by permission of The Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 29, no. 2 (2016): 72–81, doi:10.5670/oceanog.2016.40.The strong salinity stratification in the upper 50–80 m of the Bay of Bengal affects the response of the upper ocean to surface heat fluxes. Using observations from November to December 2013, we examine the effect of surface cooling on the temperature structure of the ocean in a one-dimensional framework. The presence of freshwater adds gravitational stability to the density stratification and prevents convective overturning, even when the surface becomes cooler than the subsurface. This stable salinity stratification traps heat within subsurface layers. The ocean’s reluctance to release the heat trapped within these subsurface warm layers can contribute to delayed rise in surface temperature and heat loss from the ocean as winter progresses. Understanding the dispersal of freshwater throughout the bay can help scientists assess its potential for generating the anomalous temperature response. We use the Aquarius along-track surface salinity and satellite-derived surface velocities to trace the evolution and modification of salinity in the Lagrangian frame of water parcels as they move through the bay with the mesoscale circulation. This advective tracking of surface salinities provides a Lagrangian interpolation of the monthly salinity fields in 2013 and shows the evolution of the freshwater distribution. The along-trajectory rate of salinification of water as it leaves the northern bay is estimated and interpreted to result from mixing processes that are likely related to the host of submesoscale signatures observed during our field campaigns.This work was supported by the Office of Naval Research (grant N000141310451)

Seasonality and buoyancy suppression of turbulence in the Bay of Bengal

Author Posting. © American Geophysical Union, 2019. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters, 46(8), (2019):4346-4355, doi:10.1029/2018GL081577.A yearlong record from moored current, temperature, conductivity, and four mixing meters (χpods) in the northernmost international waters of the Bay of Bengal quantifies upper‐ocean turbulent diffusivity of heat (Kt) and its response to the Indian monsoon. Data indicate (1) pronounced intermittency in turbulence at semidiurnal, diurnal, and near‐inertial timescales, (2) strong turbulence above 25‐m depth during the SW (summer) and NE (winter) monsoon relative to the transition periods (compare Kt > 10−4 m2/s to Kt  ∼ 10−5 m2/s, and (3) persistent suppression of turbulence (Kt < 10−5 m2/s) for 3 to 5 months in the latter half of the SW monsoon coincident with enhanced near‐surface stratification postarrival of low‐salinity water from the Brahmaputra‐Ganga‐Meghna delta and monsoonal precipitation. This suppression promotes maintenance of the low‐salinity surface waters within the interior of the bay preconditioning the upper northern Indian Ocean for the next year's monsoon.This work was supported by the U.S. Office of Naval Research (ONR) Grants N00014‐14‐1‐0236 and N00014‐17‐1‐2472, and the Ocean Mixing and Monsoon program of the Indian Ministry of Earth Sciences. The deployment of the Woods Hole Oceanographic Institution mooring and RW and JTF were supported by ONR Grant N00014‐13‐1‐0453. The deployment and recovery of the mooring were carried out by RV Sagar Nidhi and RV Sagar Kanya, respectively, with the help of the crew and science parties. Thanks to National Institute of Ocean Technology (India) for buoy support. The authors acknowledge invaluable discussions with Johannes Becherer, Deepak Cherian, and Sally Warner at CEOAS, OSU, and Dipanjan Chaudhuri, J Sree Lekha, and Debasis Sengupta at CAOS, IISc. The authors thank two anonymous reviewers for their detailed reviews, which have helped sharpen many aspects of this paper. Data can be accessed as described in section S2.2019-10-0

Observations and modeling of a hydrothermal plume in Yellowstone Lake

Author Posting. © American Geophysical Union, 20XX. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Geophysical Research Letters 46(12), (2019): 6435-6442, doi:10.1029/2019GL082523.Acoustic Doppler current profiler and conductivity‐temperature‐depth data acquired in Yellowstone Lake reveal the presence of a buoyant plume above the “Deep Hole” hydrothermal system, located southeast of Stevenson Island. Distributed venting in the ~200 × 200‐m hydrothermal field creates a plume with vertical velocities of ~10 cm/s in the mid‐water column. Salinity profiles indicate that during the period of strong summer stratification the plume rises to a neutral buoyancy horizon at ~45‐m depth, corresponding to a ~70‐m rise height, where it generates an anomaly of ~5% (−0.0014 psu) relative to background lake water. We simulate the plume with a numerical model and find that a heat flux of 28 MW reproduces the salinity and vertical velocity observations, corresponding to a mass flux of 1.4 × 103 kg/s. When observational uncertainties are considered, the heat flux could range between 20 to 50 MW.The authors thank Yellowstone National Park Fisheries and Aquatic Sciences, The Global Foundation for Ocean Exploration, and Paul Fucile for logistical support. This research was supported by the National Science Foundation grants EAR‐1516361 to R. S., EAR‐1514865 to K. L., and EAR‐1515283 to R. H. and J. F. All work in Yellowstone National Park was completed under an authorized Yellowstone research permit (YELL‐2018‐SCI‐7018). CTD and ADCP profiles reported in this paper are available through the Marine Geoscience Data System (doi:10.1594/IEDA/324713 and doi:10.1594/IEDA/324712, accessed last on 17 April 2019, respectively).2019-11-0

Assessing sexual harassment policy communication and impact at sea

A white paper form of J. Winter’s Oregon State University Master of Science Project.Field research is a particularly precarious work setting in which gendered harassment is perpe-trated (Clancy et al., 2014). Ocean scientists rely on research vessels to access the field, and the marine sector has its own risks associated with it. Research has found that women experience sexual harassment while working at sea on cargo ships (Thomas, 2006; Pike et al., 2021), as cadets at the U.S. Merchant Mariner Academy (United States Merchant Marine Academy, 2015), and in other positions while working at sea (Women in Ocean Science C.I.C., 2021; Österman and Boström, 2022). Research vessels– a field site at sea– merge the associated risks of the marine sector and field research. Multiple institutions own or operate research vessels, including state and federal agencies, universities and research institutes, and private foundations. In addition, any vessel, such as a commercial fishing vessel, may become a research vessel temporarily by being contracted for this purpose. This white paper is intended to better understand communication, training, implementation, and the experience of policies within the U.S. Academic Research Fleet (U.S. ARF), including Title IX and institution-specific harassment policies. The results presented here stem from a mixed methods study conducted in 2019-2021 that combined a survey of scientists and ship personnel who work onboard U.S. ARF vessels with semi-structured interviews of sexual harassment policymakers and those responsible for implementation of sexual harassment policy in the ocean sciences. We identify themes that have implications for the design and implementation of harassment policies at sea and provide the results of this study for the community within this white paper. The U.S. ARF is comprised of federally-owned vessels that are operated by academic insti-tutions and consortiums. Formed in 1972, the University National Oceanographic Laboratory System (UNOLS) is an organization of academic institutions and national laboratories, which includes U.S. ARF operating institutions, that seeks 1) to coordinate access to oceanographic research facilities including scheduling of ships within the U.S. ARF, 2) to review the current match of facilities to the needs of academic oceanographic programs, and 3) to foster support for academic oceanography (UNOLS Charter, adopted in December 2021). UNOLS does not have a mandate to create or enforce policies; however, UNOLS can influence an institution’s policy by providing an organizing structure to address community concerns. For example, the Maintaining an Environment of Respect Aboard Ships (MERAS) Committee aims to foster an environment of respect and cultivate an inclusive culture within the U.S. ARF by providing recommendations to the UNOLS community of vessel operators and users. MERAS was established in 2017 as a transition of the Pregnancy, Privacy, and Harassment Committee that first formed in 2015

A critical scale in plankton aggregations across coastal ecosystems

We examined the characteristics of biological patches at four different locations to assess the relationship of patch vertical scale, amplitude, and persistence. In contrast to patches of larger animals, we found that the majority of coherent aggregations of plankton at each site were vertically compressed, with most smaller than 5m vertically. A subset of these layers, often referred to as thin layers in the literature, was distinguished by high intensity and greater persistence but not thickness. Our results suggest that similar to 5m is a critical vertical scale below which aggregations of plankton frequently occur, pointing toward a controlling characteristic or a process common to a variety of regions and organism types. Given the commonality of this scale, insights into physical-biological dynamics gleaned from previous studies of the most intense and persistent of these patches may be applied more generally, leading to a better understanding of the ecosystem effects of heterogeneous plankton distributions.Keywords: spatial structure, patchiness, scale, plankto