Variability in satellite winds over the Benguela upwelling system during 1999–2000

Wind stress variability over the Benguela upwelling system is considered using 16 months (01 August 1999 to 29 November 2000) of satellite-derived QuikSCAT wind data. Variability is investigated using a type of artificial neural network, the self-organizing map (SOM), and a wavelet analysis. The SOM and wavelet analysis are applied to an extracted data set to find that the system may be divided into six discrete wind regimes. The wavelet power spectra for these wind regions span a range of frequencies from 4 to 64 days, with each region appearing to contain distinct periodicities. To the north, 10°–23.5°S, the majority of the power occurs during austral winter, with a 4–16 day periodicity. Further investigation of National Centers for Environmental Prediction reanalysis outgoing longwave radiation data indicates that the winter intensification of wind stress off the Angolan coast is linked with convective activity over equatorial West Africa. The summer activity appears to be linked with the intensification of the Angolan heat low. Convective activity over the Congo basin appears to impact upon wind stress variability, off the Angolan coast, throughout the year. Farther south, 24°– 35°S, the majority of the power occurs in the summer. Here a bimodal distribution occurs, with peaks of 4–12 and 25–50 days. The southernmost regions appear to be forced at higher frequencies by both midlatitude cyclones (austral winter) and mesoscale coastal lows (austral summer). At lower frequencies, eastward propagating periodic wind events that originate over eastern South America appear to be important to the forcing of wind stress over the southern Benguela

Evolution of Broader Impacts

This work is supported by the National Science Foundation under grant number OIA-1810732 and MCB-1940655, the Kavli Foundation and the Burroughs Wellcome Fund. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation, the Kavli Foundation or Burroughs Wellcome Fund

Physical and biological variability in the Antarctic Polar Frontal Zone: report on research cruise 103 of the MV SA Agulhas

A detailed hydrographic and biological survey was carried out in the region of the South-west Indian Ridge during April 2002. Hydrographic data revealed that the Andrew Bain Fracture Zone, centred at 30oE, 50oS, functions as an important choke point to the flow of the Antarctic Circumpolar Current, resulting in the convergence of the Antarctic Polar Front (APF) and the southern branch of the Sub-Antarctic Front (SSAF). Total chlorophyll-a concentration and zooplankton biomass were highest at stations occupied in the vicinity of two frontal features represented by the APF and SSAF. These data suggest that the region of the South-west Indian Ridge is an area of elevated biological activity and probably acts as an important offshore feeding area for the top predators on the Prince Edward Islands

On the seasonality of waters below the seasonal thermocline in the Gulf of Cádiz

This work examines the seasonal thermohaline variability in the Gulf of Cádiz (SW Iberian Peninsula) based on 2009–2020 repeated hydrographic observations. Subsurface water types are assorted within the mixing triangle formed by Mediterranean and Eastern North Atlantic Central Waters (ENACW). A sharp interface between 400-500 m depth separates the saline Mediterranean Overflow Waters (MOW) from the ENACW salinity minimum siting atop. The water column is warmer and more saline in winter (cooler, fresher in summer). Maximum differences of up to 0.6 ∘C and 0.15 emanate from the ENACW/MOW interface. Changes appear related to the wind-driven seasonal alternation of vertical displacement of isopycnals and poleward-equatorward transports. Upwelling-favorable winds in summer steer positive Ekman pumping velocities, which seem responsible for cooling over the ENACW salinity minimum. Below, the warm, saline signal of subtropical waters from the Azores current is attenuated by the summer approach of cooler, fresher waters from the Portugal Current system. The change of sign of Ekman pumping in winter suggests subsidence of isopycnals and warming/salinification under the seasonal thermocline. Seasonal thermohaline changes of waters leaving the Mediterranean Sea are insufficient to explain the variations under the ENACW/MOW interface. Rather, variability of Atlantic waters entrained by the overflow seem to dictate these differences.Postprint2,08

The Making of a Productivity Hotspot in the Coastal Ocean

Highly productive hotspots in the ocean often occur where complex physical forcing mechanisms lead to aggregation of primary and secondary producers. Understanding how hotspots persist, however, requires combining knowledge of the spatio-temporal linkages between geomorphology, physical forcing, and biological responses with the physiological requirements and movement of top predators.) off the Baja California peninsula, Mexico.We have identified the set of conditions that lead to a persistent top predator hotspot, which increases our understanding of how highly migratory species exploit productive regions of the ocean. These results will aid in the development of spatially and environmentally explicit management strategies for marine species of conservation concern

The resolution sensitivity of the South Asian monsoon and Indo-Pacific in a global 0.35◦ AGCM

The South Asian monsoon is one of the most significant manifestations of the seasonal cycle. It directly impacts nearly one third of the world’s population and also has substantial global influence. Using 27-year integrations of a high-resolution atmospheric general circulation model (Met Office Unified Model), we study changes in South Asian monsoon precipitation and circulation when horizontal resolution is increased from approximately 200 to 40 km at the equator (N96 to N512, 1.9 to 0.35◦). The high resolution, integration length and ensemble size of the dataset make this the most extensive dataset used to evaluate the resolution sensitivity of the South Asian monsoon to date. We find a consistent pattern of JJAS precipitation and circulation changes as resolution increases, which include a slight increase in precipitation over peninsular India, changes in Indian and Indochinese orographic rain bands, increasing wind speeds in the Somali Jet, increasing precipitation over the Maritime Continent islands and decreasing precipitation over the northern Maritime Continent seas. To diagnose which resolution related processes cause these changes we compare them to published sensitivity experiments that change regional orography and coastlines. Our analysis indicates that improved resolution of the East African Highlands results in the improved representation of the Somali Jet and further suggests that improved resolution of orography over Indochina and the Maritime Continent results in more precipitation over the Maritime Continent islands at the expense of reduced precipitation further north. We also evaluate the resolution sensitivity of monsoon depressions and lows, which contribute more precipitation over northeast India at higher resolution. We conclude that while increasing resolution at these scales does not solve the many monsoon biases that exist in GCMs, it has a number of small, beneficial impacts

A recent increase in global wave power as a consequence of oceanic warming

Wind-generated ocean waves drive important coastal processes that determine flooding and erosion. Ocean warming has been one factor affecting waves globally. Most studies have focused on studying parameters such as wave heights, but a systematic, global and long-term signal of climate change in global wave behavior remains undetermined. Here we show that the global wave power, which is the transport of the energy transferred from the wind into sea-surface motion, has increased globally (0.4% per year) and by ocean basins since 1948. We also find long-term correlations and statistical dependency with sea surface temperatures, globally and by ocean sub-basins, particularly between the tropical Atlantic temperatures and the wave power in high south latitudes, the most energetic region globally. Results indicate the upper-ocean warming, a consequence of anthropogenic global warming, is changing the global wave climate, making waves stronger. This identifies wave power as a potentially valuable climate change indicator.Funding for this project was partly provided by RISKOADAPT (BIA2017-89401-R) Spanish Ministry of Science, Innovation and Universities and the ECLISEA project part of the Horizon 2020 ERANET ERA4CS (European Research Area for Climate Services) 2016 Call