Reduction in meridional heat export contributes to recent Indian Ocean warming

Since 2000, the Indian Ocean has warmed more rapidly than the Atlantic or Pacific. Air-sea fluxes alone cannot explain the rapid Indian Ocean warming, which has so far been linked to an increase in temperature transport into the basin through the Indonesian Throughflow (ITF). Here, we investigate the role that the heat transport out of the basin at 36°S plays in the warming. Adding the heat transport out of the basin to the ITF temperature transport into the basin, we calculate the decadal mean Indian Ocean heat budget over the 2010s. We find that heat convergence increased within the Indian Ocean over 2000-2019. The heat convergence over the 2010s is the same order as the warming rate, and thus the net air-sea fluxes are near zero. This is a significant change from previous analyses using trans-basin hydrographic sections from 1987, 2002, and 2009, which all found divergences of heat. A two year time series shows that seasonal aliasing is not responsible for the decadal change. The anomalous ocean heat convergence over the 2010s compared to previous estimates is due to changes in ocean currents at both the southern boundary (33%) and the ITF (67%). We hypothesize that the changes at the southern boundary are linked to an observed broadening of the Agulhas Current, implying that temperature and velocity data at the western boundary are crucial to constrain heat budget changes.

Stratigraphic and tectonic framework of Late Cretaceous and Paleogene strata of southern Aotea Basin, northwest New Zealand

<p>Seismic reflection data reveal thick sediment sequences of Late Cretaceous to Paleogene age in the region northwest of Taranaki Basin. A new stratigraphic framework for latest Cretaceous and Paleogene strata is created based on stacking patterns and stratal termination relationships of seismic reflectors. Sequence-bounding reflectors are tied to petroleum exploration wells, including recently-drilled Romney-1, to assign age and paleoenvironment interpretation. I identify the following sequences: (1) a late Haumurian to Teurian (68 – 56 Ma) aggradational shelf sequence, with at least two regressional events linked to eustatic sea-level falls; (2) a diachronous deepening of the basin that progressed from north to south during the late Waipawan to Heretaungan (53 – 46 Ma); (3) small-scale volcanism at the southern boundary with Taranaki Basin is contemporaneous with this deepening; (4) a prograding delta on Challenger Plateau during the Porangan to Runangan (46 – 35 Ma) that is evidence for tectonic uplift of the basin margins; and (5) an onlapping sequence from latest Runangan to present (35 – 0 Ma) that indicates Challenger Plateau subsided 1,300 m. A revised set of paleogeography maps and generalised stratigraphic chart summarise these observations. The Eocene phase (52-46 Ma) of tectonic subsidence and diffuse volcanism is one of the earliest signs of tectonic activity associated with development of the Cenozoic plate boundary through New Zealand. Petroleum system analysis reveals that southern Aotea Basin is prospective for petroleum exploration, with 3 plays identified in the Late Haumurian to Teurian (79 – 56 Ma) strata, in spite of Romney-1 proving unsuccessful.</p>

Stratigraphic and tectonic framework of Late Cretaceous and Paleogene strata of southern Aotea Basin, northwest New Zealand

<p>Seismic reflection data reveal thick sediment sequences of Late Cretaceous to Paleogene age in the region northwest of Taranaki Basin. A new stratigraphic framework for latest Cretaceous and Paleogene strata is created based on stacking patterns and stratal termination relationships of seismic reflectors. Sequence-bounding reflectors are tied to petroleum exploration wells, including recently-drilled Romney-1, to assign age and paleoenvironment interpretation. I identify the following sequences: (1) a late Haumurian to Teurian (68 – 56 Ma) aggradational shelf sequence, with at least two regressional events linked to eustatic sea-level falls; (2) a diachronous deepening of the basin that progressed from north to south during the late Waipawan to Heretaungan (53 – 46 Ma); (3) small-scale volcanism at the southern boundary with Taranaki Basin is contemporaneous with this deepening; (4) a prograding delta on Challenger Plateau during the Porangan to Runangan (46 – 35 Ma) that is evidence for tectonic uplift of the basin margins; and (5) an onlapping sequence from latest Runangan to present (35 – 0 Ma) that indicates Challenger Plateau subsided 1,300 m. A revised set of paleogeography maps and generalised stratigraphic chart summarise these observations. The Eocene phase (52-46 Ma) of tectonic subsidence and diffuse volcanism is one of the earliest signs of tectonic activity associated with development of the Cenozoic plate boundary through New Zealand. Petroleum system analysis reveals that southern Aotea Basin is prospective for petroleum exploration, with 3 plays identified in the Late Haumurian to Teurian (79 – 56 Ma) strata, in spite of Romney-1 proving unsuccessful.</p>

Initial assessment of the groundwater flow and budget using Geographic Information System, MODFLOW-2005 and the FREEWAT modeling tool in Bouteldja coastal aquifer (Northern East of Algeria)

The Bouteldja coastal aquifer is one of the most important groundwater resources in North eastern of Algeria. The region is under a sub-humid climate with an average rainfall of 600-880 mm/y. The unconfined aquifer is constituted of Quaternary sands formations. The hydrogeological characteristics were determined based on previous reports. A very important inflow recharges the sandy aquifer in the Southeastern boundary, in relation to a fault network system linking the aquifer and the Obeira Lake area. Another inflow is observed at the Southern boundary in relation to the exchanges with the alluvial aquifer of Bouteldja. The purpose of the present study is to provide an initial assessment of the groundwater flow and water budget of this aquifer. To achieve this goal, a one-layer groundwater flow numerical model was developed using the MODFLOW-2005 code and the FREEWAT software, using the available data. The model was run in steady state conditions. Calibration was achieved using the piezometric measurements of May 2018 as calibration target. After several trials of manual calibrations, the model successfully simulated the groundwater flows directions and heads. Calibration efforts lead to an acceptable concordance (for the purpose of this study) between the estimated and calculated hydraulic conductivity and piezometric heads, except at the Eastern border. The analyses of the simulated inflow budget shows that aside the rainfall infiltration, exchanges with surface water bodies, the adjoining alluvial aquifer and the fault system provide a relevant amount of water. This significant recharge needs additional investigations. This numerical modeling exercise using MODFLOW, the FREEWAT software and GIS reached the objective of a preliminary description of the groundwater flow and it represents an acceptable starting point for more thorough hydrodynamic characterization of the Bouteldja coastal aquifer.

Northeastern part of the Bilanivske ferruginousquartzite quarry: Risks of mining allotment

Purpose.Substantiation of the managerial decisions to minimize the risks of mining the Bilanivske ferruginous quartzite quarry on its northeastern margin. Methods. The legislative, methodological, cartographic and literary materials on the topic, as well as the area of survey have been analyzed. The necessary cartographic plotting and calculations have been performed. An abstract-logical method is used to formulate conclusions and theoretical generalizations. Findings. The ecological risks of the Bilanivske quarry northeastern margin have been substantiated: presence of uranium ore deposits and a radioactive anomaly; geochemical pollution of groundwater; a depression cone, large in area and in depth, can be formed in the region; a probability of using explosives when mining the field; use of the Bilanivske quarry eastern side for laying mine shafts and adits. The question is raised about the expected expansion of the Bilanivske quarry boundaries to the east during its mining, as well as falling into the sanitary protection zone boundaries of the northwestern residential community of the Nova Haleshchyna urban-type settlement. It is recommended, when mining the Bilanivske and Kremenchuk (Haleshchynske) iron ore deposits, to develop for them a unified draft Environmental Impact Assessment (EIA) and a unified draft of sanitary protection zone, taking into account the fact of their mutual influence on the environment. Originality.For the first time, based on a combination of geological, mining, technological and spatial factors, a site (zone) of mutual risks has been identified in the Bilanivske and Kremenchuk (Haleshchynske) iron ore deposits development. The site has an area of 165 ha, bounded by the northeastern side of the Bilanivske quarry and the southern boundary of the planned Haleshchynske mine. Practical implications.The research results can substantiate the need to resettle the residents from the northwestern residential community of the Nova Haleshchyna urban-type settlement, taking into account the Bilanivske field development by the open-pit method. In addition, they also can serve as a basis for resolving disputes between these residents and the administration of Ferrexpo Belanovo Mining LLC (Bilanivske Mining Plant).

Java Volcanic Arc, what lies beneath?

Java Island is an active volcanic arc that resides in the southwestern - southern boundary of Sundaland edges. The volcanic arc consists of several volcanism episodes, with a relatively younging trend northward (Late Oligocene to Pleistocene), following the Indo-Australian plates inward migration. In contrast to the prolific neighboring Northwest and Northeast Java Basins in the Northern edges of Java Island; the basin reconstruction and development in the East-West trending depression in median ranges of Java (from Bogor to Kendeng Troughs) are overlooked and lays bare the challenge to the seismic imaging due to the structural complexity of the overthrusted Neogene unit as well as immense Quaternary volcanic eruption covers. On the other hand, oil and gas seepages around the northern and central parts of the Island confirmed the active petroleum generation. Five focused window areas are selected for this study. A total of 1,893 Km sections, 584 rock samples, 1569 gravity, and magnetic data, and 29 geochemical samples (rocks, oil, and gas samples) were acquired during the study. Geological fieldwork was focused on the stratigraphic unit composition and the observable features of deformation products from the outcrops. Due to the scarcity of the Paleogene deposit exposure in the Central-East Java area, the rock samples were also collected from the mud volcano ejected materials in the Sangiran Dome. Both Bogor and Kendeng Troughs are active petroleum systems that generate type II /III Kerogen typical to the reduction organic material derived from transition to the shallow marine environment. The result suggests that these basins are secular from the neighboring basins, The Northwest and Northeast Java Basins, characterized by oxidized terrigenous type III Kerogen. The contrasting subsurface configuration between Bogor and Kendeng Troughs mainly concerns the fold-thrust belt basement involvement and the tectonic shortening effect on the formerly rift basin.

Fe-binding organic ligands in coastal and frontal regions of the western Antarctic Peninsula

Organic ligands are a key factor determining the availability of dissolved iron (DFe) in the high-nutrient low-chlorophyll (HNLC) areas of the Southern Ocean. In this study, organic speciation of Fe is investigated along a natural gradient of the western Antarctic Peninsula, from an ice-covered shelf to the open ocean. An electrochemical approach, competitive ligand exchange – adsorptive cathodic stripping voltammetry (CLE-AdCSV), was applied. Our results indicated that organic ligands in the surface water on the shelf are associated with ice-algal exudates, possibly combined with melting of sea ice. Organic ligands in the deeper shelf water are supplied via the resuspension of slope or shelf sediments. Further offshore, organic ligands are most likely related to the development of phytoplankton blooms in open ocean waters. On the shelf, total ligand concentrations ([Lt]) were between 1.2 and 6.4 nM eq. Fe. The organic ligands offshore ranged between 1.0 and 3.0 nM eq. Fe. The southern boundary of the Antarctic Circumpolar Current (SB ACC) separated the organic ligands on the shelf from bloom-associated ligands offshore. Overall, organic ligand concentrations always exceeded DFe concentrations (excess ligand concentration, [L′] = 0.8–5.0 nM eq. Fe). The [L′] made up to 80 % of [Lt], suggesting that any additional Fe input can be stabilized in the dissolved form via organic complexation. The denser modified Circumpolar Deep Water (mCDW) on the shelf showed the highest complexation capacity of Fe (αFe'L; the product of [L′] and conditional binding strength of ligands, KFe'Lcond). Since Fe is also supplied by shelf sediments and glacial discharge, the high complexation capacity over the shelf can keep Fe dissolved and available for local primary productivity later in the season upon sea-ice melting.