Modelling wind-driven inter-ocean exchange in the greater Agulhas with the regional ocean modelling system

Includes bibliographical references.Two Regional Ocean Modelling System configurations, AGIO and ARC112, are developed to investigate (1) the structure of the Agulhas leakage, (2) the dynamical link between the leakage and the Agulhas Current, and (3) the sensitivity of this link to changes in the regional wind field. Both configurations span the Indian Ocean and South East Atlantic Ocean (29° W - 115° E, 48.25° S - 7.5° N) at 1/4° resolution. ARC112 includes a two-way, AGRIF nested, 1/12° child domain, encapsulating the Agulhas retroflection (0° E - 40° E, 45.5° S - 29.5° S). Model evaluation shows that the basin-scale circulation patterns of the South Indian Ocean are appropriately captured. Western boundary transports match those derived from in situ hydrography, though source region fluxes exceed those observed. Both configurations exhibit inertially governed retroflections and produce Agulhas rings with eddy kinetic energy patterns consistent with those derived from altimetry. Improved topography in ARC112 yields a retroflection position and leakage value closer to observations. Dominant regional water masses are captured, but discrepancies in their distributions remain, especially in highly turbulent areas. The interannual variability of upper ocean heat content is well captured, and Indian Ocean dipole modes are appropriately expressed. Leakage is shown to be confined to the top 1500 m. Flux estimates, derived using complementary Eulerian passive tracer and Lagrangian virtual float techniques, converge where retroflection position is more accurate. Eddy flux, isolated using an Okubo-Weiss parameterisation, contributes only 1/3 to the total flux at the GoodHope line, with a 2:1 anticyclone to cyclone ratio. The remaining intra-ring flux occurs due to mixing between rings in the Cape Basin thermocline, which contains up to 50% Indian Ocean waters. Using a hybrid-criteria eddy-tracking scheme, ARC112i is shown to represent all three recently identified eddy paths, producing an accurate number of rings and cyclones with trajectories and radii that mirror observations, despite higher simulated speeds. A multi-decadal strengthening of the eddy component of Agulhas leakage is ascribed to increases in anti-cyclone speed and cyclone size. Linear changes in trade wind intensity, imposed through a series of idealised wind stress anomalies, concomitantly modulate Agulhas Current transport. The leakage flux response to changing western boundary current inertia is minimal, decreasing with higher resolution. Large changes in eddy kinetic energy are associated with small leakage anomalies, suggesting that the former is a poor leakage proxy. Initially, the leakage responds linearly to increasing westerly wind intensity, but increased mixing between the Agulhas Return Current and Antarctic Circumpolar Current reduces inter-basin flux as the latter adjusts. Consequently, it is suggested that Agulhas Current and leakage magnitude may, to a degree, vary independently, and that multi-decadal trends in the region may be a function of the wind forcing used. Equatorward shifts in the zero line of wind-stress curl drive a small leakage increase, counter to proposed palaeoceanographic mechanism where leakage is implied to reduce under these conditions

The role of cryptic dispersal in shaping connectivity patterns of marine populations in a changing world

Genetic connectivity directly shapes the demographic profile of marine species, and has become one of the most intensely researched areas in marine ecology. More importantly, it has changed the way we design and describe Marine Protected Areas across the world. Population genetics is the preferred tool when measuring connectivity patterns, however, these methods often assume that dispersal patterns are 1) natural and 2) follow traditional meta-population models. In this short review, we formally introduce the phenomenon of cryptic dispersal, where multiple introductory events can undermine these assumptions, resulting in grossly inaccurate connectivity estimates. We also discuss the evolutionary consequences of cryptic dispersal and advocate for a cross-disciplinary approach that incorporates larval transport models into population genetic studies to provide a level of oceanographic realism that will result in more accurate estimates of dispersal. As globalized trade continues to expand, the rate of anthropogenic movement of marine organisms is also expected to increase and as such, integrated methods will be required to meet the inevitable conservation challenges that will arise from it

Good Health at Low Cost 25 years on: lessons for the future of health systems strengthening.

In 1985, the Rockefeller Foundation published Good health at low cost to discuss why some countries or regions achieve better health and social outcomes than do others at a similar level of income and to show the role of political will and socially progressive policies. 25 years on, the Good Health at Low Cost project revisited these places but looked anew at Bangladesh, Ethiopia, Kyrgyzstan, Thailand, and the Indian state of Tamil Nadu, which have all either achieved substantial improvements in health or access to services or implemented innovative health policies relative to their neighbours. A series of comparative case studies (2009-11) looked at how and why each region accomplished these changes. Attributes of success included good governance and political commitment, effective bureaucracies that preserve institutional memory and can learn from experience, and the ability to innovate and adapt to resource limitations. Furthermore, the capacity to respond to population needs and build resilience into health systems in the face of political unrest, economic crises, and natural disasters was important. Transport infrastructure, female empowerment, and education also played a part. Health systems are complex and no simple recipe exists for success. Yet in the countries and regions studied, progress has been assisted by institutional stability, with continuity of reforms despite political and economic turmoil, learning lessons from experience, seizing windows of opportunity, and ensuring sensitivity to context. These experiences show that improvements in health can still be achieved in countries with relatively few resources, though strategic investment is necessary to address new challenges such as complex chronic diseases and growing population expectations

The impact of ocean biogeochemistry on physics and its consequences for modelling shelf seas

We use modelling and assimilation tools to explore the impact of biogeochemistry on physics in the shelf sea environment, using North-West European Shelf (NWES) as a case study. We demonstrate that such impact is significant: the attenuation of light by biogeochemical substances heats up the upper 20 m of the ocean by up to 1 °C and by a similar margin cools down the ocean within the 20–200 m range of depths. We demonstrate that these changes to sea temperature influence mixing in the upper ocean and feed back into marine biology by influencing the timing of the phytoplankton bloom, as suggested by the critical turbulence hypothesis. We compare different light schemes representing the impact of biogeochemistry on physics, and show that the physics is sensitive to both the spectral resolution of radiances and the represented optically active constituents. We introduce a new development into the research version of the operational model for the NWES, in which we calculate the heat fluxes based on the spectrally resolved attenuation by the simulated biogeochemical tracers, establishing a two-way coupling between biogeochemistry and physics. We demonstrate that in the late spring-summer the two-way coupled model increases heating in the upper oceanic layer compared to the existing model and improves by 1–3 days the timing of the simulated phytoplankton bloom. This improvement is relatively small compared with the existing model bias in bloom timing, but is sufficient to have a visible impact on model skill in the free run. We also validate the skill of the two-way coupling in the context of the weakly coupled physical-biogeochemical assimilation currently used for operational forecasting of the NWES. We show that the change to the skill is negligible for analyses, but it remains to be seen how much it differs for the forecasts

Application of a new net primary production methodology: A daily to annual-scale data set for the North Sea, derived from autonomous underwater gliders and satellite Earth observation

Shelf seas play a key role in both the global carbon cycle and coastal marine ecosystems through the draw-down and fixing of carbon, as measured through phytoplankton net primary production (NPP). Measuring NPP in situ and extrapolating this to the local, regional, and global scale presents challenges however because of limitations with the techniques utilised (e.g. radiocarbon isotopes), data sparsity, and the inherent biogeochemical heterogeneity of coastal and open-shelf waters. Here, we introduce a new data set generated using a technique based on the synergistic use of in situ glider profiles and satellite Earth observation measurements which can be implemented in a real-time or delayed-mode system (https://doi.org/10.5285/e6974644-2026-0f94-e053-6c86abc00109; Loveday and Smyth, 2022). We apply this system to a fleet of gliders successively deployed over a 19-month time frame in the North Sea, generating an unprecedented fine-scale time series of NPP in the region. At a large scale, this time series gives close agreement with existing satellite-based estimates of NPP for the region and previous in situ estimates. What has not been elucidated before is the high-frequency, small-scale, depth-resolved variability associated with bloom phenology, mesoscale phenomena, and mixed layer dynamics

The stellar-to-halo mass relation of GAMA galaxies from 100 deg2of KiDS weak lensing data

We study the stellar-to-halo mass relation of central galaxies in the range 9.7 5 × 1010h-2M&sun;, the stellar mass increases with halo mass as ˜ {}M_h^{0.25}. The ratio of dark matter to stellar mass has a minimum at a halo mass of 8 × 1011h-1M&sun; with a value of M_h/M_*=56_{-10}^{+16} [h]. We also use the GAMA group catalogue to select centrals and satellites in groups with five or more members, which trace regions in space where the local matter density is higher than average, and determine for the first time the stellar-to-halo mass relation in these denser environments. We find no significant differences compared to the relation from the full sample, which suggests that the stellar-to-halo mass relation does not vary strongly with local density. Furthermore, we find that the stellar-to-halo mass relation of central galaxies can also be obtained by modelling the lensing signal and stellar mass function of satellite galaxies only, which shows that the assumptions to model the satellite contribution in the halo model do not significantly bias the stellar-to-halo mass relation. Finally, we show that the combination of weak lensing with the stellar mass function can be used to test the purity of group catalogues

Agulhas Leakage Predominantly Responds to the Southern Hemisphere Westerlies

The Agulhas Current plays a crucial role in the thermohaline circulation through its leakage into the South Atlantic. Under both past and present climates, the trade winds and westerlies could have the ability to modulate the amount of Indian-Atlantic inflow. Compelling arguments have been put forward suggesting that trade winds alone have little impact on the magnitude of Agulhas leakage. Here, employing three ocean models for robust analysis – a global coarse resolution, a regional eddy-permitting and a nested high-resolution eddy-resolving configuration – and systematically altering the position and intensity of the westerly wind belt in a series of sensitivity experiments, it is shown that the westerlies, in particular their intensity, control the leakage. Leakage responds proportionally to the westerlies intensity up to a certain point. Beyond this, through the adjustment of the large-scale circulation, energetic interactions occur between the Agulhas Return Current and the Antarctic Circumpolar Current that result in a state where leakage no longer increases. This adjustment takes place within 1 to 2 decades. Contrary to previous assertions, our results further show that an equatorward (poleward) shift in westerlies increases (decreases) leakage. This occurs due to the redistribution of momentum input by the winds. It is concluded that the reported present-day leakage increase could therefore reflect an unadjusted oceanic response mainly to the strengthening westerlies over the last few decades

‘Flat-capping it’: Memory, nostalgia and value in retroactive male working-class identification

The article contends that working-class identities in Britain today are increasingly positioned as ‘valueless’. Emerging from empirical research with students and staff from working-class backgrounds based in higher education institutions, the article explores how some of the male participants in the project continue to identify in class-based terms. Arguing that a tendency to dwell on the past has opened up the possibility of a ‘valuable’ identification for these participants in the present, the article focuses on the critical dimensions of nostalgia and collective memory by exploring two particular kinds of ‘mnemonic imagination’ (Pickering and Keightley, 2013): ‘flat-capping it’ and ‘family folklore’. Far from being regressive, it is concluded that a recourse to the past in this particular context can be seen as a retroactive strategy, which enables the negotiation of gendered working-class subjectivities in the present, as well as providing a critical perspective on the future for those whose classed identities are so often rendered as ‘valueless’

40-year AVHRR record of visible channel Rrs and coccolithophorid blooms, links to netCDF files

A consistently calibrated 40-year record of visible channel remote sensing reflectances (Rrs), based on the Advanced Very High Resolution Radiometer (AVHRR) sensor global time-series. The dataset is derived from the top of atmosphere visible channel reflectances provided by the Pathfinder Atmospheres - Extended (PATMOS-x) V5.3 Climate Data Record (CDR), atmospherically corrected and masked according to quality flags. Temporal filtering and selective masking of the Rrs product is used to highlight regions of the global ocean affected by highly reflective blooms of the coccolithophorid Emiliania Huxleyi over the past four decades. Both the Rrs and coccolithophorid bloom product are supplied at monthly resolution on a 0.1 x 0.1 degree global grid. Monthly mean and monthly maximum values are supplied for each product. Requests for daily files can be made to Plymouth Marine Laboratory