Hasil untuk "Oceanography"

W. S. V. Arx

C. Lalli, T. Parsons

S. Pond, G. Pickard

R. M. Reynolds

Manfred Brath, Jon Petersen, Stefan A. Buehler et al.

Abstract Atmospheric Radiative Transfer Simulator (ARTS) is an open source general purpose radiative transfer model used for a wide range of applications from remote sensing to the interaction of climate and radiation. In the past, it was confined to the microwave and infrared spectral range, as ARTS could not simulate the interaction of solar radiation in the atmosphere. Here we close this gap and extend ARTS to the shortwave range. We introduce a solar source that can be used as a collimated beam source and as background source allowing to resolve the finite solar disc. Additionally, we implemented a new clear sky solver that supports collimated beam sources and solar background sources, and updated the ARTS DISORT interface to utilize DISORT's capability for collimated beam sources. This allows consistent line‐by‐line radiative transfer simulations from the microwave to the ultraviolet range with ARTS. We evaluated the shortwave capabilities of ARTS by comparing it with LBLRTM for clear sky simulations. The root mean square deviation between them is 0.70 Wm−2 for the upward flux at top of the atmosphere and 0.66 Wm−2 for the downward flux at the surface. Simulations of a sunrise as seen from space, of satellite observations and of full spectrum all sky radiative flux illustrate the new capabilities. With the new features, ARTS can be used for a wide range of new applications.

S. Jeffrey, R. Mantoura, S. Wright

Marzia Gabriele, Raffaella Brumana, Nicola Genzano

In environmental management, monitoring transitions toward regenerative agriculture (RA) supports carbon offset initiatives aligned with Regulation (EU) 2018/841. Current Land Use, Land Use Change, and Forestry (LULUCF) platforms primarily analyze macro-scale Earth Observation (EO) vegetation trends, yet are increasingly enhancing ground-based data collection. This study integrates these approaches through a methodological workflow comprising: (1) a survey segment with a 30 × 30 m pixel sampling grid for landscape-scale trend assessment and sub-hectare Survey Validation Areas delineating specific RA management practices; and (2) an EO monitoring segment using Landsat 5, 7, and 8 time series, processed in R and Google Earth Engine (GEE) to model 30 m phenological dynamics, alongside 10 m Sentinel-2 NDVI 15-day Maximum Value Composites published via a GEE application (RegenAPP). Applied to an experimental RA site, La Junquera – Camp Altiplano (Murcia, Spain), the workflow enabled fine-scale analyses, identifying greening trends in no-till RA plots in contrast to browning in adjacent tilled organic fields. Sub-hectare analyses further detailed phenological patterns linked to specific RA practices. This integrated EO–Survey approach complements LULUCF assessments by coupling EO-derived vegetation analytics with targeted field validation, capturing spatial and temporal RA transition dynamics.

C. Kohlman, S. Mogen, J. T. Cohen et al.

Abstract Following the highly impactful 2013–2016 Marine Heatwave (MHW), another MHW occurred in the Northeast Pacific during summer 2019. While the physical drivers of this event are well described, its biogeochemical impacts remain poorly understood. We use Ocetrac, a Python package that tracks spatiotemporal extreme events, to identify physical and biogeochemical anomalies associated with the 2019 MHW within two observation‐based products, GOBAI‐O2 and MOBO‐DIC, and model output from the Community Earth System Model Forced Ocean Sea Ice Reconstruction (FOSI). Our findings reveal that warm temperature anomalies associated with the MHW negatively correlate with dissolved inorganic carbon (DIC) and dissolved oxygen (DO). Model reconstruction suggests that DIC anomalies were driven by air‐sea flux and biological processes, while anomalies in DO are linked to air‐sea flux and circulation. These results underscore the utility of new observational products and models for assessing the biogeochemical consequences of MHWs.

Huinan Kang, Yunsen Hu, Sakdirat Kaewunruen et al.

Geometric and mechanical analyses were performed on 82 selenium-rich eggs, which underwent hydrostatic testing as 2 raw eggs, 60 steamed eggs, and 20 emptied eggshells. By analyzing the geometric and mechanical properties of the egg, we can draw inspiration from its structural design to create a pressure shell capable of effectively withstanding the immense water pressure in deep-sea environments. The major axis, minor axis, egg-shape coefficient, weight, thickness, volume, superficial area, and ultimate compressive strength were measured, and their correlations were analyzed. The thickness, egg-shape coefficient, and ultimate compressive strength were normally distributed, and many parameters were strongly correlated. Moreover, finite element analysis was conducted to evaluate the compressive resistance of egg-like pressure shells made from different materials, including metal, ceramic, resin, and selenium-enriched eggshell materials. The performance ratio of the ceramic shells was 2.6 times higher than that of eggshells, and eggshells outperformed metal and resin shells by factors of 2.14 and 4.49, respectively. The eggshells had excellent compression resistance. These findings offer novel insights into the design and optimization of egg-like pressure shells.

Elian Vanderborght, Henk A. Dijkstra

The Global Overturning Circulation (GOC) is a key component of the climate system, transporting heat, carbon, and salt throughout the global ocean. Previous reduced-dimensional models have sought to represent this three-dimensional circulation but often neglected three key observational features: (1) the meridional overturning circulation is in geostrophic balance below the Ekman layer, (2) diapycnal mixing is strongly enhanced near ocean boundaries, and (3) upwelling is partly driven by adiabatic dynamics in the Southern Ocean. Building on Callies and Marotzke (2012), we develop a reduced model that consistently incorporates all three by simulating temperature in latitude-depth space along the eastern and western boundaries of a semi-enclosed basin connected in the south to a zonally periodic re-entrant channel. The model clarifies how zonal temperature differences in the basin arise and are maintained through adiabatic and diffusive processes, giving rise to the geostrophic GOC. It also provides a transparent framework for understanding how geostrophic currents cross the equator to form the interhemispheric overturning, and how boundary-intensified mixing and Southern Ocean winds regulate polar downwelling rates. The reduced model shows good agreement with both a three-dimensional ocean model and theoretical scaling laws for stratification and overturning strength. Owing to its simplicity, it is well suited for long integrations exploring the GOC response under extreme forcing scenarios and offers a useful framework for testing eddy and mixing parameterizations.

A. Bennett

R. Thomson

Nurul Magfirah Sukri, Windra Priawandiputra, Tri Atmowidi et al.

Graphical Abstract   Highlight Research • Approximately 3978 sponge individuals were collected and grouped to 137 morphospecies, with 120 of these have been identified intothree classes, 17 orders, 40 families, and at least 70 genera. • Sponges in the Makassar Strait showed significant differences based on individual abundance data. • Pannikiang Island had the greatest abundance and diversity of sponges, and the lowest found in Gusung Toraja. • The sponge composition of the three islands indicated that neighboring islands do not guarantee high similarity.     Abstract Sponges are an important and dominant component of marine benthos which are threatened due to global environmental degradation. To establish appropriate conservation policies, the diversity and distribution of sponge must be understood. Meanwhile, the availability of sponge diversity and distribution especially in the Makassar Strait, is still lacking. This study aimed to investigated the diversity and distribution of the sponges composition in coral reef ecosystems on three less-explored islands in the Makassar Strait (South and West Sulawesi provinces, Indonesia). Sponge assemblages were sampled at a depth of 5 m using Underwater Photo Transect method, with a total area of 15 m2 at each site. We recorded a total of 137 morphospecies of sponges (N = 3978 individuals), 59 of which were restricted to Barrang Caddi, 39 to Gusung Toraja, and 92 to Pannikiang. Only 12 species were shared among all islands. We found ten morphological types of sponge, with the dominant type in all islands was encrusting. Our results showed that Pannikiang island represents the  highest diversity and abundance of sponges, which had the largest area compared to the other islands and is surrounded by mangrove forests. There was a significant difference in species composition between Pannikiang and other islands.

Ashley E. Stanek, Jonathan A. O'Donnell, Michael P. Carey et al.

Abstract Climate change alters the sources and age of carbon in Arctic food webs by fostering the release of older carbon from degrading permafrost. Radiocarbon (14C) traces carbon sources and age, but data before rapid warming are rare and limit assessments over time. We capitalized on 14C data collected ~ 40 years ago that used fish as natural samplers by resampling the same species today. Among resampled fish, those using freshwater food webs had the oldest 14C ages (> 1000 yr BP), while those using marine food webs had the youngest 14C ages (near modern). One migratory species encompassed the entire range of 14C ages because juveniles fed in freshwater streams and adults fed in offshore marine habitats. Over ~ 40 yr, average 14C ages of freshwater and marine feeding fish shifted closer to atmospheric values, suggesting a potential influence from “greening of the Arctic.”

Esther Capó, James C. McWilliams, Jonathan Gula et al.

Realistic computational simulations in different oceanic basins reveal prevalent prograde mean flows (i.e. in the direction of topographic Rossby wave propagation along isobaths; a.k.a. topostrophy) on topographic slopes in the deep ocean, consistent with the barotropic theory of eddy-driven mean flows. Attention is focused on the Western Mediterranean Sea with strong currents and steep topography. These prograde mean currents induce an opposing bottom drag stress and thus a turbulent boundary-layer mean flow in the downhill direction, evidenced by a near-bottom negative mean vertical velocity. The slope-normal profile of diapycnal buoyancy mixing results in down-slope mean advection near the bottom (a tendency to locally increase the mean buoyancy) and up-slope buoyancy mixing (a tendency to decrease buoyancy) with associated buoyancy fluxes across the mean isopycnal surfaces (diapycnal downwelling). In the upper part of the boundary layer and nearby interior, the diapycnal turbulent buoyancy flux divergence reverses sign (diapycnal upwelling), with upward Eulerian mean buoyancy advection across isopycnal surfaces. These near-slope tendencies abate with further distance from the boundary. An along-isobath mean momentum balance shows an advective acceleration and a bottom-drag retardation of the prograde flow. The eddy buoyancy advection is significant near the slope, and the associated eddy potential energy conversion is negative, consistent with mean vertical shear flow generation for the eddies. This cross-isobath flow structure differs from previous proposals, and a new one-dimensional model is constructed for a topostrophic, stratified, slope bottom boundary layer. The broader issue of the return pathways of the global thermohaline circulation remains open, but the abyssal slope region is likely to play a dominant role.

David Lannes, Mathieu Rigal

This paper is devoted to the theoretical and numerical investigation of the initial boundary value problem for a system of equations used for the description of waves in coastal areas, namely, the Boussinesq-Abbott system in the presence of topography. We propose a procedure that allows one to handle very general linear or nonlinear boundary conditions. It consists in reducing the problem to a system of conservation laws with nonlocal fluxes and coupled to an ODE. This reformulation is used to propose two hybrid finite volumes/finite differences schemes of first and second order respectively. The possibility to use many kinds of boundary conditions is used to investigate numerically the asymptotic stability of the boundary conditions, which is an issue of practical relevance in coastal oceanography since asymptotically stable boundary conditions would allow one to reconstruct a wave field from the knowledge of the boundary data only, even if the initial data is not known.

D. Pham, J. Verron, M. Roubaud

Dhruv Bhagtani, Andrew McColl Hogg, Ryan Mahony Holmes et al.

Gyres are central features of large-scale ocean circulation and are involved in transporting tracers such as heat, nutrients, and carbon-dioxide within and across ocean basins. Traditionally, the gyre circulation is thought to be driven by surface winds and quantified via Sverdrup balance, but it has been proposed that surface buoyancy fluxes may also contribute to gyre forcing. Through a series of eddy-permitting global ocean model simulations with perturbed surface forcing, the relative contribution of wind stress and surface heat flux forcing to the large-scale ocean circulation is investigated, focusing on the subtropical gyres. In addition to gyre strength being linearly proportional to wind stress, it is shown that the gyre circulation is strongly impacted by variations in the surface heat flux (specifically, its meridional gradient) through a rearrangement of the ocean's buoyancy structure. On shorter timescales ($\sim$ decade), the gyre circulation anomalies are proportional to the magnitude of the surface heat flux gradient perturbation, with up to $\sim 0.15\,\mathrm{Sv}$ anomaly induced per $\mathrm{W}\,\mathrm{m}^{-2}$ change in the surface heat flux. On timescales longer than a decade, the gyre response to surface buoyancy flux gradient perturbations becomes non-linear as ocean circulation anomalies feed back onto the buoyancy structure induced by the surface buoyancy fluxes. These interactions complicate the development of a buoyancy-driven theory for the gyres to complement the Sverdrup relation. The flux-forced simulations underscore the importance of surface buoyancy forcing in steering the large-scale ocean circulation.

Ashley J. Barnes, Callum J. Shakespeare, Andy McC. Hogg et al.

Internal waves propagate on the ocean's stratification, carrying energy and redistributing momentum through the ocean. When internal waves break, they contribute to diapycnal mixing in the ocean interior, but this breaking behaviour depends upon the scale of the waves. Low-mode internal waves have larger horizontal and vertical scales, and thus break less readily than higher-mode waves. The scattering of internal waves by topography is an important mechanism in transferring internal wave energy to smaller scales that are more conducive to wave breaking and mixing processes. In this study, we propose and investigate a mechanism in which storm-generated low-mode internal waves scatter at topography. We hypothesise that horizontally propagating internal wave modes generated by strong winds (i.e., due to a storm) can rapidly dephase; these dephased waves can then be scattered from topography, resulting in higher-mode upward-propagating waves within hours of the passage of a storm. We investigate this phenomenon in an idealised numerical model of a storm passing over a prominent ridge. Bottom-scattered near-inertial internal waves propagate away from the ridge rapidly in the wake of the storm. We perform several perturbation experiments varying the properties of the ocean, the winds and the topography. The bottom-scattered waves exhibit spatial downscaling, and have an energy flux equivalent to 10% the magnitude of the energy flux from surface-generated near-inertial waves in our domain. Although small in a globally averaged sense, we argue that the topographic scatter of storm-generated near-inertial waves could account for the unexplained near-inertial wave signals found in ocean observations and numerical studies.

J. Arístegui, J. Gasol, C. M. Duarte et al.