Subtidal Inner Shelf Currents off Cartagena de Indias, Caribbean Coast of Colombia

Seasonal trends in inner shelf subtidal circulation off the coast of Cartagena de Indias, Colombia, are examined through the analysis of current profiles, hydrographic, meteorological and satellite data collected from 1999 to 2002. During the dry season (December–April) the water column is well-mixed and along-shelf currents flow southwestward following the steady trade winds. In the rainy season (May –November) the water column experiences continuous events of stratification and the along-shelf currents flow northeastward, opposing the weak southwestward winds. In the dry season the along shelfcirculation is mostly driven by wind forcing, while in the rainy season, the circulation is set by an alongshore baroclinic pressure gradient. In the cross shelfdirection upwelling conditions are observed most of the year and geostrophic balance conditions are found

Confirmation of ENSO-Southern Ocean teleconnections using satellite-derived SST

© The Author(s), 2018. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Remote Sensing 10 (2018): 331, doi:10.3390/rs10020331.The Southern Ocean is the focus of many physical, chemical, and biological analyses due to its global importance and highly variable climate. This analysis of sea surface temperatures (SST) and global teleconnections shows that SSTs are significantly spatially correlated with both the Antarctic Oscillation and the Southern Oscillation, with spatial correlations between the indices and standardized SST anomalies approaching 1.0. Here, we report that the recent positive patterns in the Antarctic and Southern Oscillations are driving negative (cooling) trends in SST in the high latitude Southern Ocean and positive (warming) trends within the Southern Hemisphere sub-tropics and mid-latitudes. The coefficient of regression over the 35-year period analyzed implies that standardized temperatures have warmed at a rate of 0.0142 per year between 1982 and 2016 with a monthly standard error in the regression of 0.0008. Further regression calculations between the indices and SST indicate strong seasonality in response to changes in atmospheric circulation, with the strongest feedback occurring throughout the austral summer and autumn.B.S.F. is supported by the NASA/South Carolina Space-grant Graduate Assistantship. A. Macdonald acknowledges support from NOAA Grant #NA160AR4310172

Ocean-Atmosphere Variability in the Northwest Atlantic Ocean During Active Marine Heatwave Years

The Northwest (NW) Atlantic has experienced extreme ecological impacts from Marine Heatwaves (MHWs) within the past decade. This paper focuses on four MHW active years (2012, 2016, 2017, and 2020) and the relationship between Sea Surface Temperature anomalies (SSTA), Sea Surface Salinity anomalies (SSSA), North Atlantic Oscillation (NAO), Geopotential Height anomalies (ZA), and anomalous Jet Stream positions (JSPA). Multichannel singular spectrum analysis (MSSA) reveals the strongest temporal covariances between SSSA and SSTA, and JSPA and SSTA for all years, particularly for 2020 (SSSA–SSTA: 50%, JSPA–SSTA: 51%) indicating that this active MHW year was more atmospherically driven, followed by 2012, which had the second highest temporal covariances (SSSA–SSTA: 47%, JSPA–SSTA: 50%) between these parameters. Spatial correlations for SSSA and SSTA between NAO during MHW active years disrupt the long–term (2010–2020) positive relationship in the NW Atlantic. SSSA and JSPA, and SSSA and SSTA were strongly correlated across the NW Atlantic; 2012 SSSA–JSPA correlations were strong and positive between 56–62°W, and 2016, 2017, and 2020 SSSA–JSPA correlations were mostly strong and negative, with strong positive correlations present near the coastline (70–66°W) or off the NW Atlantic shelf (52–48°W). SSSA–SSTA showed the opposite correlations of similar spatial distributions of SSSA–JSPA for all MHW active years. This indicates strong relationships between JSPA, SSSA, and SSTA during MHWs. Understanding the temporal and spatial interplay between these parameters will aid in better monitoring and prediction of MHWs

United States contributions to the Second International Indian Ocean Expedition (US IIOE-2)

From the Preface: The purpose of this document is to motivate and coordinate U.S. participation in the Second International Indian Ocean Expedition (IIOE-2) by outlining a core set of research priorities that will accelerate our understanding of geologic, oceanic, and atmospheric processes and their interactions in the Indian Ocean. These research priorities have been developed by the U.S. IIOE-2 Steering Committee based on the outcomes of an interdisciplinary Indian Ocean science workshop held at the Scripps Institution of Oceanography on September 11-13, 2017. The workshop was attended by 70 scientists with expertise spanning climate, atmospheric sciences, and multiple sub-disciplines of oceanography. Workshop participants were largely drawn from U.S. academic institutions and government agencies, with a few experts invited from India, China, and France to provide a broader perspective on international programs and activities and opportunities for collaboration. These research priorities also build upon the previously developed International IIOE-2 Science Plan and Implementation Strategy. Outcomes from the workshop are condensed into five scientific themes: Upwelling, inter-ocean exchanges, monsoon dynamics, inter-basin contrasts, marine geology and the deep ocean. Each theme is identified with priority questions that the U.S. research community would like to address and the measurements that need to be made in the Indian Ocean to address them.We thank the following organizations and programs for financial contributions, support and endorsement: the U.S. National Oceanic and Atmospheric Administration; the U.S. Ocean Carbon and Biogeochemistry program funded by the National Science Foundation and the National Aeronautics and Space Administration; the NASA Physical Oceanography Program; Scripps Institution of Oceanography; and the Indo-US Science and Technology Forum

A study of the Indian Ocean circulation using satellite observations and model simulations

The Indian Ocean circulation is studied using remotely-sensed satellite observations of sea surface height, sea surface temperature and surface winds to gain a more complete view of the surface circulation than is possible from hydrographic studies alone. The instruments used are, respectively, TOPEX/POSEIDON (T/P) altimeter, ERS-1 Along-Track Scanning Radiometer (ATSR) and Scatterometer during 1993-1995.The Somali eddies and possible formation mechanisms in the Arabian Sea are studied. The most energetic eddies found along the Somali coast depend on the monsoon system. The western boundary current, East India Coastal Current (EICC), in the Bay of Bengal is detected and analysed. Because of the scarcity of measured data in this region, satellite observations are required to examine the mechanisms which are involved in driving the EICC. Kelvin waves and Rossby waves in the Indian Ocean are identified and their role in energy transfer to the western boundary currents and to the eddies is examined. Kelvin and Rossby wave phase speeds are computed using two dimensional Fast Fourier Transforms (FFT) and Complex Principal Component (CPCA) Analysis. The phase speeds calculated from T/P altimetric observations are comparable to recent work by Killworth et al. (1997).A simple isopycnic N-layer wind-driven model is implemented to simulate the seasonal changes of surface and subsurface currents and circulation in the North Indian Ocean and to examine the response to different wind forcing. The solution with three active layers reproduces the robust features of the North Indian Ocean when forced with the real wind observations from the ERS-1 Scatterometer winds. As the Indian Ocean circulation depends mainly on the seasonally reversing monsoon winds, it is very important to use real winds to get a clear picture of the circulation pattern. Although most ocean models of this region are forced with climatological or ECMWF winds, in this study wind fields measured by the ERS-1 Scatterometer provide the forcing for the same period of the T/P altimeter data. The free sea surface height (FSSH) is calculated from the model at 10-day snapshots, to match the time period of the T/P altimeter cycles. The model simulations show the spaceborne scatterometers to be the most useful tool to provide wind forcing for ocean models.</p

Role of El Niño Southern Oscillation (ENSO) Events on Temperature and Salinity Variability in the Agulhas Leakage Region

This study explores the relationship between the Agulhas Current system and El Niño Southern Oscillation (ENSO) events. Specifically, it addresses monthly to yearly variations in Agulhas leakage where the Agulhas Current sheds waters into the Atlantic Ocean, in turn affecting meridional overturning circulation (MOC). Sea surface temperature (SST) data from the National Oceanic and Atmospheric Administration’s (NOAA) Advanced Very High Resolution Radiometer (AVHRR) combined with sea surface salinity (SSS) from Soil Moisture Ocean Salinity (SMOS) and Simple Ocean Data Assimilation (SODA) reanalysis are used to explore changes in Agulhas leakage dynamics. Agulhas leakage is anomalously warm in response to El Niño and anomalously cool in response to La Niña. The corresponding SSS signal shows both a primary and secondary signal response. At first, the SSS signal of Agulhas leakage is anomalously fresh in response to El Niño, but this primary signal is replaced by a secondary anomalously saline signal. In response to La Niña, the primary SSS signal of Agulhas leakage is anomalously saline, while the secondary SSS signal is anomalously fresh. The lag between the peak of ENSO and the response in SST and the corresponding primary SSS signal of Agulhas leakage is about 20 months, followed by the secondary SSS signal at a lag of about 26 months. In general, increasing ENSO strength increases the extremes of the resulting anomalous SST and SSS signal and impacts the Agulhas leakage region earlier during El Niño and slightly later during La Niña

Hurricane-driven alteration in plankton community size structure in the Gulf of Mexico: A modeling study

This was the first study to analyze phytoplankton and zooplankton community size structure during hurricane passage. A three-dimensional biophysical model was used to assess ecosystem dynamics, plankton biomass, and plankton distribution in the Gulf of Mexico during Hurricane Katrina (2005). Model simulations revealed that large phytoplankton were most responsive to hurricane-induced turbulent mixing and nutrient injection, with increases in biomass along the hurricane track. Small phytoplankton, microzooplankton, and mesozooplankton biomass primarily shifted in location and increased in spatial extent as a result of Hurricane Katrina. Hurricane passage disrupted the distribution of plankton biomass associated with mesoscale eddies. Biomass minimums and maximums that resided in the center of warm- and cold-core eddies and along eddy peripheries prior to hurricane passage were displaced during Hurricane Katrina

Satellite Data Analysis of the Upper Ocean Response to Hurricane Dorian (2019) in the North Atlantic Ocean

A suite of satellite-derived data and high-resolution ocean model outputs were used to study the response of the upper ocean to Hurricane Dorian (2019), which impacted the Bahamas and the eastern coast of the United States in August and September of 2019. We observe enhanced upwelling that in conjunction with surface cooling from precipitation led to an approximate 4 °C drop in sea surface temperature (SST) along and slightly ahead of Dorian\u27s path. The upwelling also increased the local coastal chlorophyll-a levels. Soil Moisture Active Passive (SMAP) sea surface salinity (SSS) shows a clear eye and eye wall structure on September 4 (the day of peak intensity), which has never been seen due to the recency of the SMAP satellite\u27s launch and the strength of Hurricane Dorian (2019). The initial forecast path of Hurricane Dorian was set to travel northward through central Florida; however, we can see from satellite observations that a high-pressure system in the north Atlantic redirects the path of the hurricane offshore. We show a clear upper ocean response to Hurricane Dorian using satellite observations and hope that this multiparameter approach can improve the current quantification of air-sea interactions during Category 5 conditions

Evidence of Organized Intraseasonal Convection Linked To Ocean Dynamics In the Seychelles–Chagos Thermocline Ridge

© 2018, Springer-Verlag GmbH Germany, part of Springer Nature. The Madden–Julian oscillation (MJO) is the dominant driver of intraseasonal variability across the equatorial domain of the global ocean with alternating wet and dry bands that propagate eastward primarily between 5°N and 5°S. Past research has shown that MJOs impact the surface and subsurface variability of the Seychelles–Chagos thermocline ridge (SCTR) (55°E–65°E, 5°S–12°S) located in the southwest tropical Indian Ocean (SWTIO), but investigations of how SWTIO internal dynamics may play an important role in producing MJO events remain limited. This study uses Argo, in conjunction with several remote sensing and reanalysis products, to demonstrate that SWTIO oceanic dynamics, particularly barrier layer formation and near surface heat buildup, may be associated with MJO genesis between August and December of most years between 2005 and 2013. A total of eight SWTIO specific MJO events are observed, all occurring between August and December. Four of the eight events are correlated with positive SWTIO total heat content (THC) and barrier layer thickness (BLT) interannual anomalies. Two others formed over the SWTIO during times when only one of the variables was at or above their seasonal average, while two additional events occurred when both variables experienced negative interannual anomalies. Lacking complete 1:1 correlation between the hypothesized oceanic state and the identified SWTIO MJO events, we conclude that additional work is required to better understand when variability in key oceanic variables plays a primary role in regional MJO genesis or when other factors, such as atmospheric variability, are the dominate drivers

Eddy Characteristics and Vertical Structure in the Bay of Bengal during Different Monsoon Regimes

The evolution of mesoscale eddies in the Bay of Bengal (BoB) and their characteristics (number of eddies, radius, amplitude, and eddy kinetic energy) are addressed during all strong, normal, and weak monsoon regimes from 1993 to 2019. Their impacts on the 3–7-day synoptic oscillations of atmospheric precipitation and upper ocean heat content are also assessed. In the western Bay, eddies are located in the meandering East India Coastal Current (EICC). The propagation of coastally trapped Kelvin waves into the Andaman Sea varies with monsoon intensity. Eddies with smaller radii, weaker amplitudes, increased vertical mixing, and deeper vertical extents were found during weak monsoons. Eddy kinetic energy (EKE) of EICC anticyclonic eddies is high (1200–2000 cm2 s−2) in May and November-December during weak and normal monsoon regimes, and EKE attains a maximum off the Sri Lanka coast during the strong monsoon regime. Throughout the Bay, density anomalies at ~100 m depth are influenced by subsurface temperature anomalies, while those at the surface more closely follow salinity anomalies. Wavelet coherence analysis for all three monsoon regimes reveals stronger coherence between eddy amplitude, atmospheric precipitation, and ocean heat content than the number of eddies for both anticyclonic and cyclonic eddies