A note on comonotonicity and positivity of the control components of decoupled quadratic FBSDE

In this small note we are concerned with the solution of Forward-Backward Stochastic Differential Equations (FBSDE) with drivers that grow quadratically in the control component (quadratic growth FBSDE or qgFBSDE). The main theorem is a comparison result that allows comparing componentwise the signs of the control processes of two different qgFBSDE. As a byproduct one obtains conditions that allow establishing the positivity of the control process.Comment: accepted for publicatio

Earth observation and machine learning reveal the dynamics of productive upwelling regimes on the Agulhas Bank

The combined application of machine learning and satellite observations offers a new way for analysing complex ocean biological and physical processes. Here, an unsupervised machine learning approach, Self Organizing Maps (SOM), is applied to discover links between surface current variability and phytoplankton productivity during seasonal upwelling over the Agulhas Bank (South Africa), from 23 years (November-March 1997-2020) of daily satellite observations (surface current, sea surface temperature, chlorophyll-a). The SOM patterns extracted over this dynamically complex region, which is dominated by the Agulhas Current (AC), revealed 4 topologies/modes of the AC system. An AC flowing southwestward along the shelf edge is the dominant mode. An AC with a cyclonic meander near shelf is the second most frequent mode. An AC with a cyclonic meander off shelf and AC early retroflection modes are the least frequent. These AC topologies influence the circulation and the phytoplankton productivity on the shelf. Strong (weak) seasonal upwelling is seen in the AC early retroflection, the AC with a cyclonic meander near shelf modes and in part of the AC along the shelf edge mode (the AC with a cyclonic meander off shelf mode and in part the AC along the shelf edge mode). The more productive patterns are generally associated with a strong southwestward flow over the central bank caused by the AC intrusion to the east Bank or via an anticyclonic meander. The less productive situations can be related to a weaker southwest flow over the central bank, strong northeast flow on the eastern bank, and/or to a stronger northwest flow on the central bank. The SOM patterns show marked year-to-year variability. The high/low productivity events seem to be linked to the occurrence of extreme phases in climate variability modes (El Niño Southern Oscillation, Indian Ocean Dipole)

VEGFR2 promotes central endothelial activation and the spread of pain in inflammatory arthritis

Chronic pain can develop in response to conditions such as inflammatory arthritis. The central mechanisms underlying the development and maintenance of chronic pain in humans are not well elucidated although there is evidence for a role of microglia and astrocytes. However in pre-clinical models of pain, including models of inflammatory arthritis, there is a wealth of evidence indicating roles for pathological glial reactivity within the CNS. In the spinal dorsal horn of rats with painful inflammatory arthritis we found both a significant increase in CD11b+ microglia-like cells and GFAP+ astrocytes associated with blood vessels, and the number of activated blood vessels expressing the adhesion molecule ICAM-1, indicating potential glio-vascular activation. Using pharmacological interventions targeting VEGFR2 in arthritic rats, to inhibit endothelial cell activation, the number of dorsal horn ICAM-1+ blood vessels, CD11b+ microglia and the development of secondary mechanical allodynia, an indicator of central sensitization, were all prevented. Targeting endothelial VEGFR2 by inducible Tie2-specific VEGFR2 knock-out also prevented secondary allodynia in mice and glio-vascular activation in the dorsal horn in response to inflammatory arthritis. Inhibition of VEGFR2 in vitro significantly blocked ICAM-1-dependent monocyte adhesion to brain microvascular endothelial cells, when stimulated with inflammatory mediators TNFa and VEGF-A165a. Taken together our findings suggest that a novel VEGFR2-mediated spinal cord gliovascular mechanism may promote peripheral CD11b+ circulating cell transmigration into the CNS parenchyma and contribute to the development of chronic pain in inflammatory arthritis. We hypothesise that preventing this glio-vascular activation and circulating cell translocation into the spinal cord could be a new therapeutic strategy for pain caused by rheumatoid arthritis

Absence of the Great Whirl giant ocean vortex abates productivity in the Somali upwelling region

Somali upwelling is the fifth largest upwelling globally with high productivity, attracting tuna migratory species. A key control on the upwelling productivity is its interaction with one of the world’s largest oceanic eddies, the Great Whirl inducing a strong downwelling signal. Here, we use satellite-derived observations to determine the Great Whirl impact on the extent of the upwelling-driven phytoplankton bloom. We find that following decreases in upwelling intensity, productivity has declined by about 10% over the past two decades. The bloom extent has also been diminishing with an abrupt decrease around 2006–2007, coinciding with an abrupt increase in the downwelling effect. Absent or weak Great Whirl leads to the occurrence of smaller anticyclonic eddies with a resulting downwelling stronger than when the Great Whirl is present. We suggest that 2006–2007 abrupt changes in the bloom and downwelling extents’ regimes, are likely driven by Indian Ocean Dipole abrupt shift in 2006

Marine heatwaves and cold spells in the Northeast Atlantic: what should the UK be prepared for?

Up to now, the UK has avoided major marine heatwaves (MHWs) that cause severe damage to marine ecosystems and the blue economy. However, an unprecedented in its intensity, though short-lived, MHW occurred in UK waters in June 2023. This event sounded an alarm bell, highlighting gaps in our understanding of MHW characteristics and their potential future impacts in the UK. Here, we use a combination of remote sensing data and model output to characterise MHWs and Marine Cold Spells (MCSs) around the UK and the wider North Atlantic, and to assess the potential for concurrent biogeochemical extreme events. Results indicate that across the wider North Atlantic, the UK is not a hot spot for MHWs or MCSs but, regionally, the southern North Sea experiences the most activity. This is also the location of extreme chlorophyll-a concentrations, here termed blue waves (low chlorophyll-a) and green waves (high chlorophyll-a). However, there is not a very pronounced relationship between temperature and chlorophyll-a extremes, which may be impacted by the exact location, drivers and season of occurrence. In contrast, the southern North Sea and English Channel may experience a MHW and low near-bottom oxygen compound events year-round, which, due to the combination of thermal stress and reduced oxygen availability, may negatively impact benthic marine ecosystems. While MHWs in UK waters do not appear to be as long-lasting or intense as other well-documented events around the world, they are projected to increase. Thus, the UK has a unique opportunity to learn from other nations and so develop robust and comprehensive policies to increase preparedness and response capability for future extreme events

Cold spells, fresh waves, and the biogeochemical response in the North Atlantic Cold Anomaly region

Regional effects of marine cold spells (MCS, periods of anomalous cooling), their impact on ecosystem biogeochemistry, and link to salinity extremes remain underexplored. A case in point is North Atlantic's Cold Anomaly (CA) region (known as the “cold blob”), which hits record low temperatures during 2014–16 while most of the global ocean warmed. Using up to 42 years of observations, we characterize the CA as a manifestation of both MCS and Fresh Waves (FW, low salinity extremes) and analyze the surface biogeochemical response. We observe a quasiperiodic pattern of MCS from the 1980s and FW (at least) from the 1990s to early 2020s in the CA region with alternations from cool and freshwater to warm and saline conditions. Since 1990s, the CA region appears to be potentially undergoing MCS and FW compound events that are more frequent and prolonged but less intense than other North Atlantic areas. The 2014-16 CA was among the most widespread and prolonged MCS and FW events associated with a deeper mixed layer and distinct biogeochemical signature, including elevated nutrients and oxygen, an overall increased chlorophyll-a and intensified ocean acidification. These results suggest that MCS could mitigate certain climate change effects through cooling and enhanced productivity, while exacerbating others such as ocean acidification. We compare 2014–16 CA region effects with those of Pacific's warm blob, identifying contrasting behaviors from physical processes to biogeochemical impacts and discussing a common atmospheric driver. Our findings emphasize the need to further study ecological responses to MCS in the North Atlantic

Retention properties of the Agulhas bank and their relevance to the chokka squid life cycle

Retention is thought to be a crucial component required to create a favourable habitat for coastal pelagic species. It is vital for the survival of ‘chokka’ squid (Loligo reynaudii), which is a fishery that supports thousands of people living in the Eastern Cape of South Africa. After chokka spawn, retention on the Agulhas Bank is crucial to prevent starvation in the early life stages. Using a high-resolution ocean model, this study quantifies retention properties of the Agulhas Bank most relevant to the chokka squid. We estimate the proportion of virtual Lagrangian particles, representing paralarvae, that are retained on the Agulhas Bank within 30 days after being released from the main chokka squid spawning sites. Over an 18-year period (1995–2013), considerable variability is found on seasonal and interannual timescales, with the greatest retention occurring for particles released further to the west. The greater losses for the easternmost release sites are due to increased interaction with the Agulhas Current. While 90–100% retention is the most common scenario, high loss (>50%) events are also apparent and are associated with different variability modes of the Agulhas Current. These variability modes include i) meanders that cause offshore flow at the northeast edge of the Bank, ii) the presence of a fast, onshore branch of the Agulhas Current rapidly advecting the particles off the Bank further west (associated with a Natal Pulse) and iii) an Agulhas Current positioned further south of the Bank leading to an offshore flow from the eastern Agulhas Bank. The third variability mode usually occurs 1–2 months after the passage of a Natal Pulse or meander. However, 1–2 weeks after the passage of a Natal Pulse, retention increases, so the timing of these events relative to particle release is crucial. This shows that the key to understanding paralarvae retention lies both in the occurrence of these dynamic features and in their timing relative to the spawning events

Spatial and temporal variability of net primary production on the Agulhas Bank, 1998–2018

Despite the importance of Agulhas Bank (AB) marine productivity in supporting South African coastal fisheries and shelf ecosystems, there are relatively few regional-scale assessments of its spatial and temporal variability, and most productivity studies have been limited in scale. Here we use satellite-derived Net Primary Production (NPP) rates calculated using the Vertically Generalized Production Model (VGPM) to examine the spatial and temporal dynamics of NPP over the 21-year satellite record (1998–2018) on the AB. In calculating VGPM NPP we used the OCCI Chlorophyll-a product, SST from Operational-Sea-Surface-Temperature-and-Sea-Ice-Analysis (OSTIA) and PAR from GlobColour level-3 mapped products as these represent the longest datasets that fit our extended study period. We examine spatial trends between the eastern and central AB, as well as three areas of the bank (around Port Alfred, the Tsitsikamma coast, and the ‘cold ridge’) that have been previously identified as contributing significantly to the overall productivity of the AB. The AB shows only a moderate degree of seasonality in NPP calculated from the VGPM, with NPP being highest in austral summer (1.7–1.8 g C m−2 d−1) and lowest in winter (0.9–1.0 g C m−2 d−1), and remains relatively high (>1 g C m−2 d−1) throughout the year, contrasting sharply with other shelf systems. Considered annually, NPP on the bank was 516 g C m−2 yr−1 (38 Mt C yr−1 when scaled to the total shelf area) which is higher than many other shelf systems though lower than the neighbouring Benguela system and is indicative of a moderately productive shelf system fuelled by perennial NPP. Comparing different sections of the AB from east to central bank, and including the three upwelling areas, highlighted that spatial differences in NPP were relatively limited; that these three upwelling areas made similar contributions to their relative proportion of the total shelf area, and that average rates of NPP are spatially similar across the bank, though notable high rates occur in some coastal upwelling areas. Interannual variability in NPP was relatively modest, varying between years by only ∼15% over the two decades assessed. Over the 21-year data set, there was a slight (∼0.26% yr−1) statistically-significant decline in calculated NPP over time for the AB as a whole, which, when examined on a pixel-by-pixel basis, indicated that most of the decline was on the central bank between 100 m and 200 m isobaths. In summer, an increase in NPP occurred on the EAB (26.5–28°E). In conclusion, the AB is a significant site of perennial moderate levels of NPP, varying little interannually and with only a slight decline in NPP over time. These factors lead to a stable environment in terms of ecosystem productivity so that the AB makes a significant contribution to the productivity of South African regional fisheries

Interannual monsoon wind variability as a key driver of East African small pelagic fisheries

Small pelagic fisheries provide food security, livelihood support and economic stability for East African coastal communities—a region of least developed countries. Using remotely- sensed and field observations together with modelling, we address the biophysical drivers of this important resource. We show that annual variations of fisheries yield parallel those of chlorophyll-a (an index of phytoplankton biomass). While enhanced phytoplankton biomass during the Northeast monsoon is triggered by wind-driven upwelling, during the Southeast monsoon, it is driven by two current induced mechanisms: coastal “dynamic uplift” upwelling; and westward advection of nutrients. This biological response to the Southeast monsoon is greater than that to the Northeast monsoon. For years unaffected by strong El-Niño/La-Niña events, the Southeast monsoon wind strength over the south tropical Indian Ocean is the main driver of year-to-year variability. This has important implications for the predictability of fisheries yield, its response to climate change, policy and resource management

Australia’s COVID-19 pandemic housing policy responses

This research reviewed Australia’s COVID-19 housing policy responses to better understand their intervention approach, underlying logic, short and long term goals, target groups and level of success. It considered literature and policy from Australia and a small number of international comparator policies; conducted online surveys of landlords and of economists; and consulted key stake holders. Given Australia’s federated system of government, considerable differences quickly emerged between intervention approaches across states and territories. This was also driven by the extent to which different jurisdictions were impacted by the spread of the virus, the extent and frequency of lockdowns, and damage to state/local economies. The national and state policy measures implemented to support home ownership achieved the desired goal of providing short-term stimulus to the residential building sector and support to the broader economy. However, a range of anticipated and unforeseen consequences have precipitated as a result of concentrated demand-side subsidies, low interest rates and flexible lending conditions. The establishment of an agile infrastructure to support information sharing will support more effective and innovative housing policy development in the future. The state-to-state infrastructure and approaches that were developed rapidly and which supported jurisdictional responses to COVID-19 provide a template for a shelf-ready policy-sharing practice that warrants supported development across governments. This could usefully include local government as well as state and territory and national tiers of governance