Description: To model tracer spreading in the ocean, Lagrangian simulations in an offline framework are a practical and efficient alternative to solving the advective–diffusive tracer equations online. Differences in both approaches raise the question of whether both methods are comparable. Lagrangian simulations usually use model output averaged in time, and trajectories are not subject to parameterized subgrid diffusion, which is included in the advection–diffusion equations of ocean models. Previous studies focused on diffusivity estimates in idealized models but could show that both methods yield similar results as long as the deformations-scale dynamics are resolved and a sufficient amount of Lagrangian particles is used. This study compares spreading of an Eulerian tracer simulated online and a cloud of Lagrangian particles simulated offline with velocities from the same ocean model. We use a global, eddy-resolving ocean model featuring 1/20° horizontal resolution in the Agulhas region around South Africa. Tracer and particles were released at one time step in the Cape Basin and below the mixed layer and integrated for 3 years. Large-scale diagnostics, like mean pathways of floats and tracer, are almost identical and 1D horizontal distributions show no significant differences. Differences in vertical distributions, seen in a reduced vertical spreading and downward displacement of particles, are due to the combined effect of unresolved subdaily variability of the vertical velocities and the spatial variation of vertical diffusivity. This, in turn, has a small impact on the horizontal spreading behavior. The estimates of eddy diffusivity from particles and tracer yield comparable results of about 4000 m2 s−1 in the Cape Basin.

Description: Sea surface height (SSH) variability in the tropical Pacific is determined by surface fluxes of which momentum flux is the most important one. The new atmospheric forcing data set JRA-55-do (Tsujino, H. et al. (submitted)) offers the chance of an improved representation of tropical SSH variability. We present a comparison of SSH variability of the tropical Pacific in two global ORCA025 (Nemo3.6) configurations, forced with COREv2 and JRA-55-do atmospheric datasets. While the amplitude of SSH variability in COREv2-runs is in close agreement with altimeter observations, a reduced interannual variability of wind stress in JRA-55-do leads to weaker SSH-variability in the tropical Pacific. A lagged correlation analyses of SSH with climate indices such as ENSO or Southern Oscillation shows a higher agreement between JRA-55-do and altimeter observations than between COREv2 and observations, suggesting an improved representation of the processes that determine SSH variability

Description: The Makassar Strait, the main passageway of the Indonesian Throughflow (ITF), is an important component of Indo-Pacific climate through its inter-basin redistribution of heat and freshwater. Observational studies suggest that wind-driven freshwater advection from the marginal seas into the Makassar Strait modulates the strait's surface transport. However, direct observations are too short (〈15 years) to resolve variability on decadal timescales. Here we use a series of global ocean simulations to assess the advected freshwater contributions to ITF transport across a range of timescales. The simulated seasonal and interannual freshwater dynamics are consistent with previous studies. On decadal timescales, we find that wind-driven advection of South China Sea (SCS) waters into the Makassar Strait modulates upper-ocean ITF transport. Atmospheric circulation changes associated with Pacific decadal variability appear to drive this mechanism via Pacific lower-latitude western boundary current interactions that affect the SCS circulation. Key Points: - A global ocean model is used to show how freshwater impacts the decadal variability of transport through the main Indonesian Throughflow pathway - Wind-driven advection of South China Sea freshwater induces an upstream pressure gradient that reduces transport - Freshwater input is modulated by atmospheric circulation changes associated with Pacific decadal variability

Description: Strong regional sea-level trends, mainly related to basin-wide wind stress anomalies, have been observed in the western tropical Pacific over the last 3 decades. Analyses of regional sea level in the densely populated regions of the neighbouring Australasian Mediterranean Sea (AMS; also called tropical Asian seas) are hindered by its complex topography and respective studies are sparse. We used a series of global eddy-permitting ocean models, including a high-resolution configuration that resolves the AMS with 120∘ horizontal resolution, forced by a comprehensive atmospheric forcing product over 1958–2016 to characterize the patterns and magnitude of decadal sea-level variability in the AMS. The nature of this variability is elucidated further by sensitivity experiments with interannual variability restricted to either the momentum or buoyancy fluxes, building on an experiment employing a repeated-year forcing without interannual variability in all forcing components. Our results suggest that decadal fluctuations of the El Niño–Southern Oscillation (ENSO) account for over 80 % of the variability in all deep basins of the region, except for the central South China Sea (SCS). Changes related to the Pacific Decadal Oscillation (PDO) are most pronounced in the shallow Arafura and Timor seas and in the central SCS. On average, buoyancy fluxes account for less than 10 % of decadal SSH variability, but this ratio is highly variable over time and can reach values of up to 50 %. In particular, our results suggest that buoyancy flux forcing amplifies the dominant wind-stress-driven anomalies related to ENSO cycles. Intrinsic variability is mostly negligible except in the SCS, where it accounts for 25 % of the total decadal SSH variability.

Description: Regional anomalies of steric sea level are either due to redistribution of heat and freshwater anomalies or due to ocean-atmosphere buoyancy fluxes. Interannual to decadal variability in sea level across the tropical Pacific is mainly due to steric variations driven by wind stress anomalies. The importance of air--sea buoyancy fluxes is less clear. We use a global, eddy permitting ocean model and a series of sensitivity experiments with quasi-climatological momentum and buoyancy fluxes to identify the contribution of buoyancy fluxes for interannual to decadal sea level variability in the tropical Pacific. We find their contribution on interannual timescales to be strongest in the central tropical Pacific at around 10° latitude in both hemispheres and also relevant in the very east of the tropical domain. Buoyancy flux forced anomalies are in phase with variations driven by wind stress changes but their effect on the prevailing anomalies and the importance of heat and fresh water fluxes vary locally. In the eastern tropical basin interannual sea level variability is amplified by anomalous heat fluxes, while the importance of fresh water fluxes is small and neither has any impact on decadal timescales. In the western tropical Pacific the variability on interannual and decadal timescales is dampened by both, heat and freshwater fluxes. The mechanism involves westward propagating Rossby waves that are triggered during ENSO events by anomalous buoyancy fluxes in the central tropical Pacific and counteract the prevailing sea level anomalies once they reach the western part of the basin.

Description: Juvenile sea turtles can disperse thousands of kilometers from nesting beaches to oceanic development habitats, aided by ocean currents. In the North Atlantic, turtles dispersing from American beaches risk being advected out of warm nursery grounds in the North Atlantic Gyre into lethally cold Northern European waters (e.g. around the United Kingdom). We used an ocean model simulation to compare simulated numbers of turtles that were advected to cold waters around the UK with observed numbers of turtles reported in the same area over ~5 decades. Rates of virtual turtles predicted to encounter lethal temperatures (≤10 and 15°C, mean 19% ± 2.7) and reach the UK were consistently low (median 0.83%, lower quartile 0.67%, upper quartile 1.02%), whereas there was high inter-annual variability in the numbers of dead or critically ill turtles reported in the UK. Generalized additive models suggest inter-annual variability in the North Atlantic Oscillation (NAO) index to be a good indicator of annual numbers of turtle strandings reported in the UK. We demonstrate that NAO variability drives variability in the dispersion scenarios of juvenile turtles from key nesting regions into the North Atlantic. Coastal effects, such as the number of storms and mean sea surface temperatures in the UK were significant but weak predictors, with a weak effect on turtle strandings. Further understanding how changing environmental conditions such as NAO variability and storms affect the fate of juvenile turtles is vital for understanding the distribution and population dynamics of sea turtles.

Description: Strong sea-level trends that exceeded the global mean signal several times over, have been observed in the western parts of the tropical Pacific between the early 1990s and early 2010s. These trends can be attributed to decadal and multidecadal variability and are mainly due to steric variations driven by wind-stress anomalies. This doctoral thesis aims to broaden our knowledge about these trends. Specifically, the role of ocean–atmosphere heat and freshwater fluxes and the linkage between sea-level variability in the western tropical Pacific and the densely populated region of the Australasian Mediterranean Sea (AMS) is investigated. These issues are addressed using a framework of ocean-sea-ice models that includes a newly developed high-resolution configuration named NUSA20 to resolve the fine-scale bathymetry of the AMS. To facilitate sensitivity experiments where the realistic atmospheric forcing is replaced by a repeated annual cycle, the recently introduced repeated-year-forcing approach (RYF) is evaluated. Three RYF-experiments using different annual cycles are conducted. Although the specific choice might be subject to the research question, it is shown that the experiments based on the periods from 1st May to 1st April of the years 1984/85 and 1990/91 show only minor differences and are able to characterize the model drift and transients of the hindcast simulation. Using a series of sensitivity experiments to disentangle the impacts of momentum fluxes on one side and heat and freshwater fluxes on the other side on sea-level variability, it is shown that anomalous buoyancy fluxes amplify interannual sea-level variability in the eastern tropical Pacific and that both heat and freshwater flux anomalies trigger westward propagating sea-level anomalies in the central Pacific that dampen variability on interannual and decadal timescales in the western part of the basin. In the AMS decadal fluctuations of the large-scale climate modes of the Pacific are found to account the majority of the low-frequency sea-level variability in almost all deep basins of the region. Intrinsic variability is negligible except in the South China Sea, where it accounts for up to 25 % of the total decadal sea-level variability. Overall, this thesis provides an assessment and a practical application of the RYF-approach. Building on sensitivity experiments, corresponding reference simulations and a high-resolution configuration the importance of ocean–atmosphere buoyancy fluxes for sea-level variability and the close dependence of decadal sea-level variability in the AMS on low-frequency fluctuations of Pacific climate modes is demonstrated.

Description: Marine heatwaves along the coast ofWestern Australia, referred to as Ningaloo Niño, have had dramatic impacts on the ecosystem in the recent decade. A number of local and remote forcing mechanisms have been put forward, however little is known about the depth structure of such temperature extremes. Utilizing an eddy-active global Ocean General Circulation Model, Ningaloo Niño and the corresponding cold Ningaloo Niña events are investigated between 1958-2016, with focus on their depth structure. The relative roles of buoyancy and wind forcing are inferred from sensitivity experiments. Composites reveal a strong symmetry between cold and warm events in their vertical structure and associated large-scale spatial patterns. Temperature anomalies are largest at the surface, where buoyancy forcing is dominant and extend down to 300m depth (or deeper), with wind forcing being the main driver. Large-scale subsurface anomalies arise from a vertical modulation of the thermocline, extending from the western Pacific into the tropical eastern Indian Ocean. The strongest Ningaloo Niños in 2000 and 2011 are unprecedented compound events, where long-lasting high temperatures are accompanied by extreme freshening, which emerges in association with La Niñas, more common and persistent during the negative phase of the Interdecadal Pacific Oscillation. It is shown that Ningaloo Niños during La Nina phases have a distinctively deeper reach and are associated with a strengthening of the Leeuwin Current, while events during El Niño are limited to the surface layer temperatures, likely driven by local atmosphere-ocean feedbacks, without a clear imprint on salinity and velocity.

Description: Changes in the Atlantic Meridional Overturning Circulation (AMOC) represent a crucial component of Northern Hemisphere climate variability. In modelling studies decadal overturning variability has been attributed to the intensity of deep winter convection in the Labrador Sea. This linkage is challenged by transport observations at sections across the subpolar gyre. Here we report simulations with an eddy-rich ocean model which captures the observed concentration of downwelling in the northeastern Atlantic and the negligible impact of interannual variations in Labrador Sea convection during the last decade. However, the exceptionally cold winters in the Labrador Sea during the first half of the 1990s induced a positive AMOC anomaly of more than 20%, mainly by augmenting the downwelling in the northeastern North Atlantic. The remote effect of excessive Labrador Sea buoyancy forcing is related to rapid spreading of mid-depth density anomalies into the Irminger Sea and their entrainment into the deep boundary current off Greenland.

Description: BACKGROUND Younger survivors (YS) of breast cancer often report more survivorship symptoms such as fatigue, depression, sexual difficulty, and cognitive problems than older survivors (OS). This study sought to determine the effect of breast cancer and age at diagnosis on quality of life (QoL) by comparing 3 groups: 1) YS diagnosed at age 45 years or before, 2) OS diagnosed between 55 and 70, and 3) for the YSs, age-matched controls (AC) of women not diagnosed with breast cancer. METHODS Using a large Eastern Cooperative Oncology Group (ECOG) database, 505 YS were recruited who were aged 45 years or younger when diagnosed and 622 OS diagnosed at 55 to 70 years of age. YS, OS, and AC were compared on physical, psychological, social, spiritual, and overall QoL variables. RESULTS Compared to both AC and to OS, YS reported more depressive symptoms ( P  = .005) and fatigue ( P  〈 .001), poorer self-reported attention function ( P  〈 .001), and poorer sexual function ( P  〈 .001) than either comparison group. However, YS also reported a greater sense of personal growth ( P  〈 .001) and perceived less social constraint ( P  〈 .001) from their partner than AC. CONCLUSIONS YS reported worse functioning than AC relative to depression, fatigue, attention, sexual function, and spirituality. Perhaps even more important, YS fared worse than both AC and OS on body image, anxiety, sleep, marital satisfaction, and fear of recurrence, indicating that YS are at greater risk for long-term QoL problems than survivors diagnosed at a later age. Cancer 2014. © 2014 American Cancer Society .