Stolarz, Timothy. Understanding ocean highways: trends in surface currents and divergence in urbanized coastal margins for a predictable ocean. Retrieved from https://doi.org/doi:10.7282/t3-5mcz-f550
DescriptionIn the New York – New Jersey Bight, research involving surface currents is available. However, research focusing on divergence is limited. This study focused on determining trends in surface current divergence in the New York – New Jersey Bight. This dataset consists of a 10-year span (2007–2016) of 5 MHz High Frequency Radar (HF Radar) surface current velocity profiles. For this study, the data was broken down into the following partitions: a 10-year mean, 10 annual means, 4 seasonal means, and 12 monthly means. For each year, the velocity means were split both seasonally and monthly, and the surface currents were then averaged during those periods, allowing for qualitative visual analysis on the resulting maps. For the purposes of this analysis, divergence values are represented as an upwelling vertical velocity and convergence values are represented as a downwelling vertical velocity [Manderson et al., 2011] in m/day.
Findings indicate persistent upwelling at the head of the Hudson Shelf Valley (HSV) with average vertical velocities averaging 0.15 m/day throughout the 10-year period. In the mid-shelf, there is high inter-annual and inter-seasonal variability leading to low average values of divergence (± 0.10 m/day) due to constant shifts in the divergence or convergence. This strong variability phenomenon is seen most prominently in the cross-shelf divergence patterns of the New York – New Jersey Bight, with prevalent cross-shelf divergence in the winter, spring, and fall. In the far-shelf, there tends to be along-shelf divergence patterns between the 50 – 80 m isobath from velocities increasing as the shelf deepens toward the 200 m isobath likely due to increasing velocities of the Shelfbreak Jet. Winter is the only season to be prominently upwelling of all the seasons which can be attributed to the intense cross shelf winds found during the winter.
Areas of persistent divergence such as the head of the HSV can create regions of bioproductivity leading to increases in species richness, recruitment success rates, and potential formation of harmful algal blooms. Cross-shelf ‘bridges’ of divergent flows can facilitate the cross-shelf migrations of anadromous and catadromous species along with regular cross-shelf migrators such as the bluefish.