Drivers of spring and summer variability in the coastal ocean offshore of Cape Cod, MA

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): 1789–1805, doi:10.1002/2015JC011252.The drivers of spring and summer variability within the coastal ocean east of Cape Cod, Massachusetts, a critical link between the Gulf of Maine and Mid-Atlantic Bight, are investigated using 2 years of shipboard and moored hydrographic and velocity observations from 2010 and 2011. The observations reveal sharp differences in the spring transition and along-shelf circulation due to variable freshwater and meteorological forcing, along with along-shelf pressure gradients. The role of the along-shelf pressure gradient is inferred using in situ observations of turbulent momentum flux, or Reynolds stresses, estimated from the ADCP-based velocities using recently developed methods and an inversion of the along-shelf momentum balance. During spring, the locally relevant along-shelf pressure gradient contains a sizable component that is not coupled to the along-shelf winds and often opposes the regional sea level gradient. Together with the winds, local pressure gradients dominate along-shelf transport variability during spring, while density-driven geostrophic flows appear to match the contribution of the local winds during summer. These results suggest that local effects along the Outer Cape have the potential to cause significant changes in exchange between the basins.NOAA. Grant Number: NA10OAR4170083; Woods Hole Oceanographic Institution2016-09-1

Shelf water and chlorophyll export from the Hatteras slope and outer shelf

© The Author(s), 2014. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Journal of Geophysical Research: Oceans 119 (2014): 4291–4304, doi:10.1002/2014JC009809.Using high-resolution data acquired from a shipboard ADCP and a towed Scanfish equipped with a CTD and fluorometer, we examine the properties and transport of Middle Atlantic Bight (MAB) shelf water over a region of the Hatteras outer shelf and slope where MAB shelf water is commonly deflected offshore and entrained into the Gulf Stream. The data are from a period in early August 2004 when the seasonal pycnocline of the MAB is well developed and situated over a weakly stratified, near-bottom shelf water mass commonly referred to as the cold pool. Our data show chlorophyll-rich cold pool water carried rapidly southward over the slope and outer shelf, at a rate of up to 60 cm s−1, as part of the shelf-edge frontal jet. This southward transport of chlorophyll-rich cold pool water is shunted eastward and entrained into the Gulf Stream. However, the latitude band over which this export occurs varies significantly over the 7 day course of our study, a variation which is linked to an order 50 km shift in the latitude at which the Gulf Stream separates from the continental margin. The coupled rapid translation of the Gulf Stream frontal separation and the cold pool export zone is likely to have a significant impact on the movement and accumulation of biogenic material over the Hatteras slope and rise.This work was supported by the U.S. National Science Foundation through grants OCE-03–27249 and OCE-0926999

Dynamics of the direct intrusion of Gulf Stream ring water onto the Mid-Atlantic Bight shelf

© The Author(s), 2015. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Geophysical Research Letters 42 (2015): 7687–7695, doi:10.1002/2015GL065530.Onshore intrusions of offshore waters onto the Mid-Atlantic Bight shelf can greatly affect shelf circulation, biogeochemistry, and fisheries. Previous studies have concentrated on onshore intrusions of slope water. Here we present a direct intrusion of Gulf Stream warm-core ring water onto the shelf representing a previously unknown exchange process at the shelfbreak. Impingement of warm-core rings at the shelfbreak generates along-isobath intrusions that grow like Pinocchio's nose, extending hundreds of kilometers to the southwest. By combining satellite and Ocean Observatory Initiative Pioneer Array data and idealized numerical simulations, we discover that the intrusion results from topographically induced vorticity variation of the ring water, rather than from entrainment of the shelfbreak frontal jet. This intrusion of the Gulf Stream ring water has important biogeochemical implications and could facilitate migration of marine species across the shelfbreak barrier and transport low-nutrient surface Gulf Stream ring water to the otherwise productive shelfbreak region.National Science Foundation Grant Number: OCE-112912

Length scale of the finite-amplitude meanders of shelfbreak fronts

Author Posting. © American Meteorological Society, 2015. This article is posted here by permission of American Meteorological Society for personal use, not for redistribution. The definitive version was published in Journal of Physical Oceanography 45 (2015): 2598–2620, doi:10.1175/JPO-D-14-0249.1.Through combining analytical arguments and numerical models, this study investigates the finite-amplitude meanders of shelfbreak fronts characterized by sloping isopycnals outcropping at both the surface and the shelfbreak bottom. The objective is to provide a formula for the meander length scale that can explain observed frontal length scale variability and also be verified with observations. Considering the frontal instability to be a mixture of barotropic and baroclinic instability, the derived along-shelf meander length scale formula is [b1/(1 + a1S1/2)]NH/f, where N is the buoyancy frequency; H is the depth of the front; f is the Coriolis parameter; S is the Burger number measuring the ratio of energy conversion associated with barotropic and baroclinic instability; and a1 and b1 are empirical constants. Initial growth rate of the frontal instability is formulated as [b2(1 + a1S1/2)/(1 + a2αS1/2)]NH/L, where α is the bottom slope at the foot of the front, and a2 and b2 are empirical constants. The formulas are verified using numerical sensitivity simulations, and fitting of the simulated and formulated results gives a1 = 2.69, b1 = 14.65, a2 = 5.1 × 103, and b2 = 6.2 × 10−2. The numerical simulations also show development of fast-growing frontal symmetric instability when the minimum initial potential vorticity is negative. Although frontal symmetric instability leads to faster development of barotropic and baroclinic instability at later times, it does not significantly influence the meander length scale. The derived meander length scale provides a framework for future studies of the influences of external forces on shelfbreak frontal circulation and cross-frontal exchange.WGZ and GGG were supported by the National Science Foundation through Grant OCE-1129125.2016-04-0

Richard W. Garvine (1940 –2007)

Richard Garvine passed away on December 10, 2007 of pancreatic cancer, and the ocean science community lost a respected, humane leader whose impact will endure on several levels. Rich was born in 1940 in Pottstown, Pennsylvania. His undergraduate degree in aerospace engineering at M.I.T. was followed by a Ph.D. at Princeton University in 1965, also in aerospace engineering. He was hired by the General Electric Space Sciences Laboratory as a theoretical aerodynamicist, but in 1969, perhaps prodded by a downturn in the aerospace field, he made the rather dramatic shift to a position as an Assistant Professor of Oceanography at the University of Connecticut. At this time, oceanography was booming, with growing budgets and overwhelming optimism about its future. For example, Vice President Humphrey had just visited an oceanographic institution, the Stratton Commission had recently completed its historical work calling for a greater investment in ocean activities, and the National Science Foundation was responding by the creation of the International Decade for Ocean Exploration (IDOE). It was a splendid time to enter the field, and Rich was one of many talented scientists entering with a doctorate in a specialty other than oceanography..

Scientific rationale and conceptual design of a process-oriented shelfbreak observatory: the OOI pioneer array

© The Author(s), 2019. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Gawarkiewicz, G., & Plueddemann, A. J. Scientific rationale and conceptual design of a process-oriented shelfbreak observatory: The OOI pioneer array. Journal of Operational Oceanography, 13(1), (2019): 19-36, doi: 10.1080/1755876X.2019.1679609.The Ocean Observatories Initiative (OOI) of the National Science Foundation in the USA includes a coastal observatory called the OOI Pioneer Array, which is focused on understanding shelf/slope exchange processes. The OOI Pioneer Array has been designed and constructed and is currently in operation. In order to fully understand the design principles and constraints, we first describe the basic exchange processes and review prior experiments in the region. Emphasis is placed on the space and time scales of important exchange processes such as frontal meandering and warm core ring interactions with the Shelfbreak Front, the dominant sources of variability in the region. The three major components of the Pioneer Array are then described, including preliminary data from the underwater gliders and Autonomous Underwater Vehicle (AUV) deployments. The relevance of the Pioneer Array to important recent scientific issues in the area, including enhanced warming of the continental shelf and increasing frequency and spatial extent of Gulf Stream interactions with the continental shelf is discussed. Finally, similar observatories in Asia are briefly described, and general conclusions regarding principles that should guide the design of shelfbreak observatories in other geographic regions are presented.Financial support for this work was provided by the National Science Foundation under grant number OCE-1657853 (GG) and OCE-1026342 (AJP). GG was also supported by a Senior Scientist Chair from the Woods Hole Oceanographic Institution

Shelfbreak frontal eddies over the continental slope north of Cape Hatteras

Author Posting. © American Geophysical Union, 2009. 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 114 (2009): C02017, doi:10.1029/2007JC004642.Shelfbreak and slope eddies have been implicated as important agents in the exchange of water between the shelf and slope domains of the Middle Atlantic Bight (MAB). Here we present temperature, salinity, and velocity data from a series of shipboard transects that intercepted a rich eddy field over the slope of the southern MAB. Attention is focused on a well-sampled cyclonic eddy, of roughly 60-km diameter and 300-m depth, that translated southward at 0.1 m s−1. The eddy was composed of a mix of water masses including MAB shelf and slope water, Gulf Stream water, and water from the MAB shelfbreak front. Gradient Richardson numbers suggest that these water masses were subject to vigorous turbulent vertical mixing. The transport of shelfbreak frontal water contained within the eddy was substantial. In the upper 100 m, shelfbreak frontal water comprised ∼75% of the eddy's volume. This frontal water fraction moved southward with a transport of ∼0.4 Sv, comparable with the volume transport within the shelfbreak frontal jet. A number of factors indicate that this highly energetic eddy, with maximum azimuthal velocity of 0.7 m s−1, was generated through instability of the shelfbreak frontal jet. The eddy had apparently developed rapidly (in <3 days), consistent with models of eddy generation through baroclinic instability of the shelfbreak frontal jet. The eddy's potential temperature/salinity (θ/S) properties and energy density closely matched the θ/S properties and energy density found in the frontal jet to the north of the eddy.This work was supported by the U.S. National Science Foundation through grant OCE-03-27249

Observing larval transport processes affecting population connectivity : progress and challenges

Author Posting. © Oceanography Society, 2007. This article is posted here by permission of Oceanography Society for personal use, not for redistribution. The definitive version was published in Oceanography 20, 3 (2007): 40-53.Population connectivity is inherently bio-physical: it is determined by physical transport and dispersion, as well as biological processes such as timing of spawning, larval behavior, and mortality. Knowledge of connectivity is essential for understanding ecosystem responses to changing environmental conditions. It establishes the spatial scales over which a population is connected, and in turn the primary spatial scale of population interactions and ecosystem dynamics. Concepts in population connectivity were initially developed in terrestrial ecology, where dispersal may occur at different life stages. In the simplest form, a one-dimensional dispersal curve describes the distribution of settlers away from a source region as a function of distance. As this spatial distribution varies in time, the “dispersal kernel” defines a spatial probability density function of settlers aggregated over time (see, e.g., Okubo and Levin, 2002). This dispersal kernel may be three dimensional, but is often reduced to two dimensions (e.g., animals on a plain) or one dimension (e.g., animals living along the land-water interface).GG received support from the Director of Research at WHOI. SGM is grateful to NSF Ocean Sciences for their support through grants OCE0425312, OCE 0452800, and OCE 0622967. JLL thanks NSF Ocean Sciences for support through grants OCE-9907884, OCE-0326110, and OCE-0528575 and the State of California for support through the Coastal Ocean Current Mapping Program (State Coastal Conservancy)—a component of CeNCOOS, the Central and Northern California Ocean Observing System

Mesoscale and submesoscale shelf-ocean exchanges initialize an advective marine heatwave

Author Posting. © American Geophysical Union, 2022. 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 127(1), (2022): e2021JC017927, https://doi.org/10.1029/2021JC017927.Observations and high-resolution numerical modeling are used to investigate the dynamical processes related to the initiation of an advective Marine Heatwave in the Middle Atlantic Bight of the Northwest Atlantic continental shelf. Both the observations and the model identify two significant cross-shelf intrusions in November 2016 and January 2017, with the latter inducing large-magnitude water mass anomalies across the shelf. Model prognostic fields reveal the importance of the combination of cyclonic eddies or ringlets and upwelling-favorable winds in producing the large-distance cross-shelf penetration and temperature/salinity anomalies. The cyclonic eddies in close proximity to the shelfbreak set up local along-isobath pressure gradients and provide favorable conditions for the intensification of the shelfbreak front, both processes driving cross-isobath intrusions of warm, salty offshore water onto the outer continental shelf. Subsequently, strong and persistent upwelling-favorable winds drive a rapid, bottom intensified cross-shelf penetration in January 2017 composed of the anomalous water mass off the shelfbreak. The along-shelf settings including realistic representation of bathymetric features are essential in the characteristics of the cross-shelf penetration. The results highlight the importance of smaller scale cyclonic eddies and the intricacy of the interplay between multiple processes to drive significant cross-shelf events.This work was supported by Woods Hole Oceanographic Institution (WHOI) Independent Research and Development (IR&D) award and National Oceanic and Atmospheric Administration (NOAA) Climate Program Office (CPO) Climate Variability and Predictability (CVP) program under grant NA20OAR4310398. Numerical modeling work was conducted at WHOI High-Performance Computing cluster Poseidon with startup support to Ke Chen.2022-06-0

Is biological productivity enhanced at the New England shelfbreak front?

Author Posting. © American Geophysical Union, 2013. 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 118 (2013): 517–535, doi:10.1002/jgrc.20068.A two-dimensional (cross-shelf) numerical model of the mean seasonal circulation offshore of southern New England predicts upwelling at the shelfbreak front. Expected ramifications of this upwelling include enhancement of nutrient supply, phytoplankton biomass, and productivity. However, seasonal climatologies of chlorophyll based on both in situ data and satellite observations show no mean enhancement at the front. We investigate this apparent discrepancy with a four-component planktonic ecosystem model coupled to the two-dimensional physical model. Nutrient fields are restored to climatological values at depth, and upper ocean values evolve freely according to physical and biological forcing. Vertical diffusivity is based on seasonally averaged surface and bottom mixed layer depths compiled from in situ observations. The model reproduces the general pattern of the observed cross-shelf and seasonal variations of the chlorophyll distribution. It predicts a local enhancement of phytoplankton productivity at the shelfbreak in spring and summer as a result of the persistently upwelled nutrient-rich slope water. In the model, zooplankton grazing prevents accumulation of phytoplankton biomass at the site of the upwelling. The predicted enhancement of primary productivity (but not phytoplankton biomass) at the shelfbreak constitutes a hypothesis that could be tested in the future with suitable measurements from regional long-term observatories, such as the Ocean Observatories Initiative Pioneer Array.WGZ was supported by the Woods Hole Oceanographic Institution (WHOI) postdoctoral scholarship program, the WHOI Coastal Ocean Institute, and the National Science Foundation through grant OCE-1129125. DJM and GGG were supported by ONR grant N00014-06-1-0739. DJM gratefully acknowledges support of WHOI’s H. W. Jannasch Chair.2013-07-3