The ocean’s response to stochastic atmospheric forcing

This thesis presents a series of investigations of the impact of high-frequency and small-scale atmospheric forcing on the ocean. Starting with a case study in the central Arabian Sea, a one-dimensional ocean mixed layer model is used to examine the ocean response to observed sub-daily atmospheric variability. Results show that including sub-daily atmospheric variability lowers the daily-mean sea surface temperature (SST) and damps its variability, but has little systematic effect on SST diurnal variability. This research is generalised by considering high-frequency variability via a stochastic component embedded in the atmospheric forcing and undertaking an ensemble of mixed-layer (ML) model simulations to explore the role of ML variation in generating a rectification effect on the SST. Different ML variations are engineered by tuning the solar penetration depth and comparing to a slab model where the ML depth is fixed. The SST rectification only emerges when the ML depth variation is included, and its magnitude is controlled by the background ML heat capacity that is associated with the solar penetration depth. Finally, we use a novel stochastic parameterization to represent spatially coherent mesoscale weather systems in atmospheric forcing fields. The stochastic parameterization adds high-frequency meso-scale variability to improve the ‘effective resolution’ of the atmospheric forcing fields and ‘fix’ the kinetic energy spectra. We conduct ocean model simulations with and without this realistic atmospheric forcing and find that the addition of the mesoscale forcing leads to coherent patterns of change in the SST and ML depth, which leads to statistically significant increases in transport in the subtropical and subpolar gyres in North Atlantic and in the Atlantic Meridional Overturning Circulation (AMOC). An elevated northward heat transport across the gyre boundary, driven by the enhanced subtropical gyre, slows down the subpolar gyre after about 10 years and slightly weakens the AMOC. This thesis illustrates that the high-frequency and mesoscale atmospheric variability can not only modulate local ocean status via one-dimensional response via the influence on the surface ML depth, but also excite non-local response of the circulation patterns that potentially influences the broader-scale ocean-atmosphere feedbacks

Effects of wave-current interaction on storm surge in the Taiwan Strait: Insights from Typhoon Morakot

The effects of wave-current interaction on storm surge are investigated by a two-dimensional wave-current coupling model through simulations of Typhoon Morakot in the Taiwan Strait. The results show that wind wave and slope of sea floor govern wave setup modulations within the nearshore surf zone. Wave setup during Morakot can contribute up to 24% of the total storm surge with a maximum value of 0.28 m. The large wave setup commonly coincides with enhanced radiation stress gradient, which is itself associated with transfer of wave momentum flux. Water levels are to leading order in modulating significant wave height inside the estuary. High water levels due to tidal change and storm surge stabilize the wind wave and decay wave breaking. Outside of the estuary, waves are mainly affected by the current-induced modification of wind energy input to the wave generation. By comparing the observed significant wave height and water level with the results from uncoupled and coupled simulations, the latter shows a better agreement with the observations. It suggests that wave-current interaction plays an important role in determining the extreme storm surge and wave height in the study area and should not be neglected in a typhoon forecast

Slowdown of Antarctic Bottom Water export driven by climatic wind and sea ice changes

Antarctic Bottom Water (AABW) is pivotal for oceanic heat and carbon sequestrations on multidecadal-to-millennial timescales. The Weddell Sea contributes nearly a half of global AABW through Weddell Sea Deep Water (WSDW) and denser underlying Weddell Sea Bottom Water (WSBW) that are form on the continental shelves via sea ice production. Here we report an observed 30% reduction of WSBW volume since 1992, with the largest decrease in the densest classes. This is likely driven by a multidecadal reduction in dense water production over southern continental shelf associated with a >40% decline in the sea ice formation rate. The ice production decrease is driven by northerly wind trend, related to a phase transition of the Interdecadal Pacific Oscillation since the early 1990s, superposed by Amundsen Sea Low intrinsic variability. These results reveal key influences on exported AABW to the Atlantic abyss and their sensitivity to large-scale, multidecadal climate variability

Unsupervised classification identifies coherent thermohaline structures in the Weddell Gyre region

The Weddell Gyre is a major feature of the Southern Ocean and an important component of the planetary climate system; it regulates air–sea exchanges, controls the formation of deep and bottom waters, and hosts upwelling of relatively warm subsurface waters. It is characterised by low sea surface temperatures, ubiquitous sea ice formation, and widespread salt stratification that stabilises the water column. Observing the Weddell Gyre is challenging, as it is extremely remote and largely covered with sea ice. At present, it is one of the most poorly sampled regions of the global ocean, highlighting the need to extract as much value as possible from existing observations. Here, we apply a profile classification model (PCM), which is an unsupervised classification technique, to a Weddell Gyre profile dataset to identify coherent regimes in temperature and salinity. We find that, despite not being given any positional information, the PCM identifies four spatially coherent thermohaline domains that can be described as follows: (1) a circumpolar class, (2) a transition region between the circumpolar waters and the Weddell Gyre, (3) a gyre edge class with northern and southern branches, and (4) a gyre core class. PCM highlights, in an objective and interpretable way, both expected and underappreciated structures in the Weddell Gyre dataset. For instance, PCM identifies the inflow of Circumpolar Deep Water (CDW) across the eastern boundary, the presence of the Weddell–Scotia Confluence waters, and structured spatial variability in mixing between Winter Water and CDW. PCM offers a useful complement to existing expertise-driven approaches for characterising the physical configuration and variability of oceanographic regions, helping to identify coherent thermohaline structures and the boundaries between them

Cytokine concentration in peripheral blood of patients with colorectal cancer

IntroductionThe role of tumour secretory cytokines and peripheral circulatory cytokines in tumour progression has received increasing attention; however, the role of tumour-related inflammatory cytokines in colorectal cancer (CRC) remains unclear. In this study, the concentrations of various cytokines in the peripheral blood of healthy controls and patients with CRC at different stages were compared.MethodsPeripheral blood samples from 4 healthy participants and 22 colorectal cancer patients were examined. Luminex beads were used to evaluate concentration levels of 40 inflammatory cytokines in peripheral blood samples.ResultsIn peripheral blood, compared with healthy controls and early stage (I + II) CRC patients, advanced CRC (III + IV) patients had increased concentrations of mononuclear/macrophage chemotactic-related proteins (CCL7, CCL8, CCL15, CCL2, and MIF), M2 polarization-related factors (IL-1β, IL-4), neutrophil chemotactic and N2 polarization-related cytokines (CXCL2, CXCL5, CXCL6, IL-8), dendritic cells (DCs) chemotactic-related proteins (CCL19, CCL20, and CCL21), Natural killer (NK) cell related cytokines (CXCL9, CXCL10), Th2 cell-related cytokines (CCL1, CCL11, CCL26), CXCL12, IL-2, CCL25, and CCL27, and decreased IFN-γ and CX3CL1 concentrations. The differential upregulation of cytokines in peripheral blood was mainly concentrated in CRC patients with distant metastasis and was related to the size of the primary tumour; however, there was no significant correlation between cytokine levels in peripheral blood and the propensity and mechanism of lymph node metastasis.DiscussionDifferent types of immune cells may share the same chemokine receptors and can co-localise in response to the same chemokines and exert synergistic pro-tumour or anti-tumour functions in the tumour microenvironment. Chemokines and cytokines affect tumour metastasis and prognosis and may be potential targets for treatment

​​Observing Antarctic Bottom Water in the Southern Ocean​

Dense, cold waters formed on Antarctic continental shelves descend along the Antarctic continental margin, where they mix with other Southern Ocean waters to form Antarctic Bottom Water (AABW). AABW then spreads into the deepest parts of all major ocean basins, isolating heat and carbon from the atmosphere for centuries. Despite AABW’s key role in regulating Earth’s climate on long time scales and in recording Southern Ocean conditions, AABW remains poorly observed. This lack of observational data is mostly due to two factors. First, AABW originates on the Antarctic continental shelf and slope where in situ measurements are limited and ocean observations by satellites are hampered by persistent sea ice cover and long periods of darkness in winter. Second, north of the Antarctic continental slope, AABW is found below approximately 2 km depth, where in situ observations are also scarce and satellites cannot provide direct measurements. Here, we review progress made during the past decades in observing AABW. We describe 1) long-term monitoring obtained by moorings, by ship-based surveys, and beneath ice shelves through bore holes; 2) the recent development of autonomous observing tools in coastal Antarctic and deep ocean systems; and 3) alternative approaches including data assimilation models and satellite-derived proxies. The variety of approaches is beginning to transform our understanding of AABW, including its formation processes, temporal variability, and contribution to the lower limb of the global ocean meridional overturning circulation. In particular, these observations highlight the key role played by winds, sea ice, and the Antarctic Ice Sheet in AABW-related processes. We conclude by discussing future avenues for observing and understanding AABW, impressing the need for a sustained and coordinated observing system

South Atlantic Ocean profile dataset: identification of near-Antarctic profiles using unsupervised classification

This dataset consists of temperature and salinity profiles taken by Argo floats (http://argo.ucsd.edu) and ship-based CTDs as recorded in the World Ocean Database (https://www.ncei.noaa.gov/products/world-ocean-database). It covers 65°W to 80°E in longitude, 85°S to 30°S in latitude (roughly the South Atlantic Ocean and a part of the Indian Ocean). In the vertical, it covers the top 1000m of the ocean. It was prepared using MITprof, which is a toolbox for Matlab: Gael Forget. (2017). gaelforget/MITprof: various updates and minor improvements (v1.0.1). Zenodo. https://doi.org/10.5281/zenodo.834078 This dataset should be considered the "initial" dataset that has been classified into five sub-groups using a profile classification model (PCM) built on Gaussian mixture modelling. The five-component PCM consists of these profile types: (1) subtropical Atlantic, (2) subtropical Indian, (3) circumpolar (more northern), (4) circumpolar (more southern), and (5) near-Antarctic

SO-WISE South Atlantic Ocean and Indian Ocean Observational Constraints

This dataset contains an initial set of curated and processed oceanographic observations collected as part of a joint effort between the EU SO-CHIC project and a UKRI Future Leaders Fellowship. It is partly intended to be used as a set of observational constraints for a Weddell Gyre region state estimate, although it can be used for more general analysis purposes as well. It has been used as part of an unsupervised clustering analysis [see Jones (2022) for software and Jones and Zhou (2022) for labelled dataset, see references]. Overall spatial and temporal coverage Latitude: 85°S-30°S Longitude: 65°W-80°E Time: 1974-2020 Contents CPOM_SSH: sea-ice corrected sea surface height CTD: temperature and salinity profiles from ship-based CTD casts FLOATS: temperature and salinity profiles from Argo floats SEALS: temperature and salinity profiles from seal-mounted profilers Stress_and_EKE: sea-ice corrected surface stress and EKE XBT: temperature and salinity profiles from expendable bathythermographs (XBTs) Profile quality control We only consider profiles with good position and time flags, as well as good temperature, salinity, and pressure measurements with good flags. Duplicated profiles are identified when multiple profiles are found within 24 hours over the same 2 km x 2 km grid cell, and only one profile within the spatio-temporal window is used. We then used the MITprof toolbox (Forget, G., 2017) to pre-process the selected profiles, re-gridding them onto 72 standard pressure levels; the vertical interval varies from 20 dbar at the surface to 100 dbar in the deep ocean. SSH processing SSH data is sea-ice corrected version provided by the Centre for Polar Observation and Modelling (CPOM) in the UK. It is composed by two satellite missions, Envisat (2004/05-2012/03) and Cryosat-2 (2010/07-2020/04). The data is available in montly along-track format. A gaussian 300km filter, ±3 std outliner removal and 0.5x0.25 deg interpolation is applied to grid the data. Intersatellite offset is removed using the overlapped period between two missions using the mean difference map. SSH is referenced to EIGEN6C4 geoid to obtain the dynamic ocean topography feild for the computation of geostrophic velocity. See the README in the Stress_and_EKE directory for more information. Sources Argo floats: http://argo.ucsd.edu World Ocean Database: https://www.ncei.noaa.gov/products/world-ocean-database MEOP-CTD Database (seal profilers): https://www.meop.net/ CDRv4 available via NSIDC: https://nsidc.org/data/G02202 Polar Pathfinder sea ice drift data via NSIDC: https://nsidc.org/data/nsidc-0116 Version This is a pre-production version, in that it has not yet been used with a state estimate

The impact of stochastic mesoscale weather systems on the Atlantic Ocean

The ocean is forced by the atmosphere on a range of spatial and temporal scales. In numerical models the atmospheric resolution sets a limit on these scales and for typical climate models mesoscale (,500 km) atmospheric forcing is absent or misrepresented. Previous studies have demonstrated that mesoscale forcing significantly affects key ocean circulation systems such as the North Atlantic subpolar gyre (SPG) and the Atlantic meridional overturning circulation (AMOC). Here we present ocean model simulations that demonstrate that the addition of realistic mesoscale atmospheric forcing leads to coherent patterns of change: a cooler sea surface in the tropical and subtropical Atlantic Ocean and deeper mixed layers in the subpolar North Atlantic in autumn, winter, and spring. These lead to robust statistically significant increases in the volume transport of the North Atlantic SPG by 10% and the AMOC by up to 10%. Our simulations use a novel stochastic parameterization-based on a cellular automata algorithm-to represent spatially coherent weather systems realistically over a range of scales, including down to the smallest resolvable by the ocean grid (;10 km). Convection-permitting atmospheric models predict changes in the intensity and frequency of mesoscale weather systems due to climate change, so representing them in coupled climate models would bring higher fidelity to future climate projections