Frontal dynamics of a buoyancy‐driven coastal current : quantifying buoyancy, wind, and isopycnal tilting influence on the Nova Scotia Current

Author Posting. © American Geophysical Union, 2018. 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 123 (2018): 4988-5003, doi:10.1029/2017JC013338.The focus of this study is on the relative roles of winds and buoyancy in driving the Nova Scotia Current (NSC) utilizing detailed hydrographic glider transects along the Halifax Line. We define a Hydrographic Wind Index (HWI) using a simplistic two‐layer model to represent the NSC and its frontal system. The HWI is based on local characteristics of the density front extracted from the glider data (e.g., frontal slope). The impact of wind‐driven isopycnal tilting on the frontal slope is estimated and corrected for to accurately scale the buoyancy‐driven component of the NSC. Observations from independent current profilers deployed across the NSC confirm that the HWI captures the low‐frequency variability of the NSC. The monthly wind‐driven flow is estimated to represent between 1.0% (±0.1%) and 48% (±1%) of the total alongshore currents, with a yearly mean of about 36% (±1%). We demonstrate that using local conditions is more appropriate to the study of buoyancy‐driven currents ranging over distances on the order of urn:x-wiley:jgrc:media:jgrc22972:jgrc22972-math-0001(100 km), compared to the traditional approach based on upstream conditions. Contrary to the traditional approach, the HWI is not affected by the advective time lag associated with the downshelf propagation of the buoyant water coming from the upstream source. However, the HWI approach requires high‐resolution data sets, as errors on the estimates of the buoyancy‐ and wind‐driven flows become large as the sampling resolution decreases. Despite being data intensive, we argue that the HWI is also applicable to multisource currents, where upstream conditions are difficult to define.Ocean Tracking Network (OTN) Grant Number: 375118-08; Natural Sciences and Engineering Research Council of Canada (NSERC); Canadian Foundation for Innovation Grant Number: 13011; Social Sciences and Humanities Research Council Grant Number: 871-2009-0001; University in Bergen through the POME exchange program2019-01-2

Pump it Up workshop report

Workshop held 28-29 September 2017, Cape Cod, MAA two-day workshop was conducted to trade ideas and brainstorm about how to advance our understanding of the ocean’s biological pump. The goal was to identify the most important scientific issues that are unresolved but might be addressed with new and future technological advances

Assessing the performance of a multi-nested ocean circulation model using satellite remote sensing and in situ observations

This study presents a multi-nested ocean circulation model developed recently for the central Scotian Shelf. The model consists of four submodels downscaling from the eastern Canadian Shelf to the central Scotian Shelf. The model is driven by tides, river discharges, and atmospheric forcing. The model results are validated against observations, including satellite remote sensing data from GHRSST and Aquarius and in situ measurements taken by tide gauges, a marine buoy, ADCPs and CTDs. The ocean circulation model is able to capture variations of sea level, hydrography and the Nova Scotia Current on timescales of days to seasons over the central Scotian Shelf. Model results are used in a process study to examine the effect of tidal mixing and wind-driven coastal upwelling in the formation of cold surface waters along the coast of Nova Scotia

EcoCTD for profiling oceanic physical-biological properties from an underway ship

Author Posting. © American Meteorological Society, 2020. 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 the Atmospheric and Oceanic Technology 37(5), (2020): 825-840, doi:10.1175/JTECH-D-19-0145.1.The study of ocean dynamics and biophysical variability at submesoscales of O(1) km and O(1) h raises several observational challenges. To address these by underway sampling, we recently developed a towed profiler called the EcoCTD, capable of concurrently measuring both hydrographic and bio-optical properties such as oxygen, chlorophyll fluorescence, and optical backscatter. The EcoCTD presents an attractive alternative to currently used towed platforms due to its light footprint, versatility in the field, and ease of deployment and recovery without cranes or heavy-duty winches. We demonstrate its use for gathering high-quality data at submesoscale spatiotemporal resolution. A dataset of bio-optical and hydrographic properties, collected with the EcoCTD during field trials in 2018, highlights its scientific potential for the study of physical–biological interactions at submesoscales.Authors would like to acknowledge Melissa Omand, Ben Pietro, and Jing He for their valuable input during the design phase of the EcoCTD, as well as for their support for deploying the EcoCTD in the field. We are grateful to Eva Alou, Andrea Carbonero, and John Allen for providing calibrated data from the shipboard CTD. Authors would also like to thank Don Peters along with Dynamics System Analysis Ltd. for facilitating access to ProteusDS and providing support in using the software. We are grateful to the crew of the RV Armstrong and NRV Alliance for their support in the field. Development of the EcoCTD is supported by the Office of Naval Research (ONR) through the CALYPSO Departmental Research Initiative (Grant N000141613130). Advanced field testing was supported by Woods Hole Oceanographic Institution internal funding. MATLAB routines for data processing are publicly available at https://github.com/mfreilich1/ecoctd_processing.2020-11-0

UCTD and EcoCTD Observations from the CALYPSO Pilot Experiment (2018): Cruise and Data Report

From May 27, 2018 to June 02, 2018, a scientific campaign was conducted in the Alboran Sea as part of an ONR Departmental Research Initiative, CALYPSO. The pilot cruise involved two ships: the R/V Socib, tasked with sampling fixed lines repeatedly, and the NRV Alliance that surveyed along the trajectory of Lagrangian platforms. A large variety of assets were deployed from the NRV Alliance, with the objective to identify coherent Lagrangian pathways from the surface ocean to interior. As part of the field campaign, an Underway-CTD (UCTD) system was used to measure vertical profiles of salinity, temperature and other properties while steaming, to achieve closely spaced measurements in the horizontal along the ship's track. Both a UCTD probe and an biooptically augmented probe, named EcoCTD, were deployed. The EcoCTD collects concurrent physical and bio-optical observations. This report focuses exclusively on the data collected by these two underway systems. It describes th e datasets collected during the pilot cruise, as well as the important processing steps developed for the EcoCTD.Funding was provided by the Office of Naval Research under Contract #N00014161313

CALYPSO 2019 Cruise Report: field campaign in the Mediterranean

This cruise aimed to identify transport pathways from the surface into the interior ocean during the late winter in the Alborán sea between the Strait of Gibraltar (5°40’W) and the prime meridian. Theory and previous observations indicated that these pathways likely originated at strong fronts, such as the one that separates salty Mediterranean water and the fresher water in owing from the Atlantic. Our goal was to map such pathways and quantify their transport. Since the outcropping isopycnals at the front extend to the deepest depths during the late winter, we planned the cruise at the end of the Spring, prior to the onset of thermal stratification of the surface mixed layer.Funding was provided by the Office of Naval Research under Contract No. N000141613130

DYNAMICS OF THE NOVA SCOTIA CURRENT AND LINKAGES WITH ATLANTIC SALMON MIGRATION PATTERNS OVER THE SCOTIAN SHELF

Over the 2008-2015 period, the Ocean Tracking Network provided unprecedented spatiotemporal coverage of the hydrography and currents along the Halifax Line (HL) on the Scotian Shelf, using several different monitoring techniques (e.g., moorings and underwater gliders). The observations are analyzed here to provide an extensive description of the physical oceanographic conditions over the Scotian Shelf, as well as the spatiotemporal variability observed over this period. The analysis of observations identifies the distribution of key water masses present along the HL. The water mass analysis demonstrates that the large warming event observed in 2012 was primarily due to the advection of already anomalously warm water from the Shelf Slope. The ocean circulation along the HL during this period is examined, with a focus on the seasonal cycle and the inter-annual variability of the Nova Scotia Current (NSC). A conceptual model is developed to investigate the main mechanisms driving the NSC. The relative roles of buoyancy-driven and wind-driven flows to the NSC are estimated at the HL to study the seasonal variability of the forcing and the relative importance of these two mechanisms in driving the NSC. Generally, the NSC is dominated by the buoyancy-driven component of the current, throughout the year and at all four transects between Cabot Strait and Cape Sable. The relative contributions of buoyancy and alongshore surface winds to the NSC’s dynamics are remarkably similar across transects having the same coastal orientation, but significantly vary where the coastline orientation changes. The newly-acquired oceanographic knowledge along the HL is also combined with acoustic detections of Atlantic salmon postsmolts coming from the Penobscot River to study the temporal and spatial distribution of the migrating fish in the context of oceanographic conditions. It is shown that postsmolts tend to be in greater abundance in the colder and fresher coastal water mass, while the abundance is not related to the direction or magnitude of local currents

Subducting filaments at fronts in the Alboran Sea: Physical, turbulent and biological evidences.

&amp;lt;p&amp;gt;Submesoscale instabilities along oceanic fronts can cause water mass intrusions from the surface mixed layer into the stratified pycnocline. These are important drivers of vertical exchange that have a potentially significant impact on the transfer of physical properties and biological tracers.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;The CALYPSO (Coherent Lagrangian Pathways from the Surface Ocean to Interior) ONR research initiative focuses on observing and understanding coherent vertical pathways by which vertical exchange occurs. The Alboran Sea (located in the south-western Mediterranean, east of Gibraltar) is well known for its strong density fronts and eddies. During a research cruise, onboard &amp;lt;em&amp;gt;R/V Pourquoi Pas? &amp;lt;/em&amp;gt;in early April 2019&amp;lt;em&amp;gt;,&amp;lt;/em&amp;gt; we found that fronts in this area support the generation of subducting filaments. Several types of observations (using CTD, uCTD, microstructure profiles, drifters and floats) were collected along numerous cross-front transects over a period of two weeks.&amp;lt;/p&amp;gt;&amp;lt;p&amp;gt;The analysis of the temperature profiles highlighted the presence of several intruding filaments moving along isopycnal surfaces in the proximity of the frontal area. The intrusion signal was also clearly visible in biophysical properties with elevated Chlorophyll-a concentrations, well below the deep chlorophyll maximum, in conjunction with high dissolved oxygen values. From a microstructure point of view, the upper and lower limits of the subducting filaments exhibited high turbulent dissipation rates, with values of O(10&amp;lt;sup&amp;gt;-7&amp;lt;/sup&amp;gt;) W/m&amp;lt;sup&amp;gt;2&amp;lt;/sup&amp;gt;. These dissipation rates are higher than what is generally observed at such depths and point to enhanced mixing activity at the boundaries of the intrusions even along isopycnal surfaces.&amp;lt;/p&amp;gt; </jats:p