Abstract
The Northeast U.S. (NEUS) continental shelf has experienced rapid warming in recent decades. Over the NEUS continental shelf, the circulation and annual cycle of heating and cooling lead to local variability of water properties. The mixed layer depth (MLD) is a key factor that determines the amount of upper ocean warming. A detailed description of the MLD, particularly its seasonal cycle and spatial patterns, has not been developed for the NEUS continental shelf. We compute the MLD using an observational dataset from the Northeast Fisheries Science Center hydrographic monitoring program. The MLD exhibits clear seasonal cycles across five eco-regions on the NEUS continental shelf, with maxima in January–March and minima in July or August. The seasonal cycle is largest in the western Gulf of Maine (71.9 ± 24.4 m), and smallest in the southern Mid-Atlantic Bight (34.0 ± 7.3 m). Spatial variations are seasonally dependent, with greatest homogeneity in summer. Interannual variability dominates long-term linear trends in most regions and seasons. To evaluate the sensitivity of our results, we compare the MLDs calculated using a 0.03 kg/m3 density threshold with those using a 0.2 °C temperature threshold. Temperature-based MLDs are generally consistent with density-based MLDs, although a small number of temperature-based MLDs are biased deep compared to density-based MLDs particularly in spring and fall. Finally, we compare observational MLDs to the MLDs from a high-resolution ocean reanalysis GLORYS12V1. While the mean values of GLORYS12V1 MLDs compare well with the observed MLDs, their interannual variability are not highly correlated, particularly in summer. These results can be a starting point for future studies on the drivers of temporal and spatial MLD variability on the NEUS continental shelf.
Highlights
The Northeast U.S (NEUS) continental shelf, which supports some of the world’s most productive and commercially valuable fisheries, has experienced significant changes in recent decades exacerbating the ef fect of long-term warming
This is especially evident in summer, when the mixed layer in the Western Gulf of Maine (WGOM) and Eastern Gulf of Maine (EGOM) makes up the smallest portion of the entire water column (6.5 ± 1.3% and 5.9 ± 1.4% in the month with the shallowest mixed layer depth (MLD)), while mixed layers on Georges Bank (GB) and in the Southern Mid-Atlantic Bight (SMAB) occupy a larger portion of the water column (12.2 ± 7.8% and 12.7 ± 4.1% in the month with the shallowest MLDs)
A description of the density-based MLD seasonal cycle has been constructed for the NEUS continental shelf based on in situ observations
Summary
The Northeast U.S (NEUS) continental shelf, which supports some of the world’s most productive and commercially valuable fisheries, has experienced significant changes in recent decades exacerbating the ef fect of long-term warming. On the other hand, Forsyth et al (2015) examined temperature measurements collected between 1977 and 2013 along the CMV Oleander section crossing the continental shelf and slope offshore of New Jersey, showing that enhanced warming is concentrated near the shelfbreak but penetrates the entire water col umn, implying a critical role of the shelfbreak front Continental Shelf Research 231 (2021) 104611 temperature, salinity, bathymetry, and geometry, complicates the study of its subsurface features (Townsend et al, 2006; Richaud et al, 2016; Bisagni et al, 2016) One such feature is the mixed layer, within which density is almost vertically uniform.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.