Biogeochemical measurements at the Antarctic Peninsula

Size-fractionated chlorophyll a and photosynthetic carbon incorporation, microbial oxygen production and respiration and particulate vertical flux were measured in January 1996 at three regions, characterized by distinct hydrographic fields and planktonic communities, of the Antarctic Peninsula: (1) a diatom-Phaeocystis sp., dominated community associated with the relatively stratified waters of the Gerlache Strait, (2) a nanoplankton-Cryptomonas sp. dominated assemblage at the Gerlache-Bransfield confluence; and (3) a nano- and picoplankton community in mixed waters of the Bransfield Strait. Despite the marked differences in both community structure and total phytoplankton biomass and primary production, and against predictions from models about trophic control of C export, the lowest respiration rates were measured at Bransfield (pico- and nanoplankton), and no difference was observed between the Gerlache (large diatoms) and Bransfield stations in relative vertical particle flux (6.4 vs. 5.1 % of suspended C; 14.9 vs. 10.4 % of net community production, respectively). Growth and loss rates of the phytoplankton population studied for each community indicate that microbial populations can be explained by in situ growth, but spatial (diatom-Phaeocystis sp., bloom) and temporal (diatom-Phaeocystis sp. bloom and nanoplankton communities) scales of study were shown to be insufficient for addressing the coupling between primary production and biogenic carbon export, especially after the appreciation of the accumulation of dissolved organic carbon in the water column. This would explain the unexpected results and highlights the necessity of including the mechanisms controlling accumulation and consumption of dissolved organic matter into conceptual models about the trophic control of C export.

Seawater carbonate chemistry and calcification rates of Porites rus and Hydrolithon onkodes in experiments of Moorea

Central to evaluating the effects of ocean acidification (OA) on coral reefs is understanding how calcification is affected by the dissolution of CO2 in sea water, which causes declines in carbonate ion concentration [CO3]2- and increases in bicarbonate ion concentration [HCO3]-. To address this topic, we manipulated [CO3]2- and [HCO3]- to test the effects on calcification of the coral Porites rus and the alga Hydrolithon onkodes, measured from the start to the end of a 15-day incubation, as well as in the day and night. [CO3]2- played a significant role in light and dark calcification of P. rus, whereas [HCO3]- mainly affected calcification in the light. Both [CO3]2- and [HCO3]- had a significant effect on the calcification of H. onkodes, but the strongest relationship was found with [CO3]2-. Our results show that the negative effect of declining [CO3]2- on the calcification of corals and algae can be partly mitigated by the use of [HCO3]- for calcification and perhaps photosynthesis. These results add empirical support to two conceptual models that can form a template for further research to account for the calcification response of corals and crustose coralline algae to OA.

Compilation of scientific results of the OASIS project

Seamounts are of great interest to science, industry and conservation because of their potential role as 'stirring rods' of the oceans, their enhanced productivity, their high local biodiversity, and the growing exploitation of their natural resources. This is accompanied by rising concern about the threats to seamount ecosystems, e.g. through over-fishing and the impact of trawling. OASIS described the functioning characteristics of seamount ecosystems. OASIS' integrated hydrographic, biogeochemical and biological information. Based on two case studies. The scientific results, condensed in conceptual and mass balanced ecosystem models, were applied to outline a model management plan as well as site-specific management plans for the seamounts investigated. OASIS addressed five main objectives: Objective 1: To identify and describe the physical forcing mechanisms effecting seamount systems Objective 2: To assess the origin, quality and dynamics of particulate organic material within the water column and surface sediment at seamounts. Objective 3: To describe aspects of the biodiversity and the ecology of seamount biota, to assess their dynamics and the maintenance of their production. Objective 4: Modelling the trophic ecology of seamount ecosystems. Objective 5: Application of scientific knowledge to practical conservation.

Revised age models and foraminiferal records obtained for the Last Interglacial period in six marine sediment cores

The dataset contains the revised age models and foraminiferal records obtained for the Last Interglacial period in six marine sediment cores: - the Southern Ocean core MD02-2488 (age model, sea surface temperatures, benthic d18O and d13C for the period 136-108 ka), - the North Atlantic core MD95-2042 (age model, planktic d18O, benthic d18O and d13C for the period 135-110 ka), - the North Atlantic core ODP 980 (age model, planktic d18O, sea surface temperatures, seawater d18O, benthic d18O and d13C, ice-rafted detritus for the period 135-110 ka), - the North Atlantic core CH69-K09 (age model, planktic d18O, sea surface temperatures, seawater d18O, benthic d18O and d13C, ice-rafted detritus for the period 135-110 ka), - the Norwegian Sea core MD95-2010 (age model, percentage of Neogloboquadrina pachyderma sinistral, sea surface temperatures, benthic d18O, ice-rafted detritus for the period 134-110 ka), - the Labrador Sea core EW9302-JPC2 (age model, percentage of Neogloboquadrina pachyderma sinistral, sea surface temperatures, benthic d18O for the period 134-110 ka).

Multi-temporal mapping of seagrass cover, species and biomass of the Eastern Banks, Moreton Bay, Australia, with links to shapefiles

The spatial and temporal dynamics of seagrasses have been studied from the leaf to patch (100 m**2) scales. However, landscape scale (> 100 km**2) seagrass population dynamics are unresolved in seagrass ecology. Previous remote sensing approaches have lacked the temporal or spatial resolution, or ecologically appropriate mapping, to fully address this issue. This paper presents a robust, semi-automated object-based image analysis approach for mapping dominant seagrass species, percentage cover and above ground biomass using a time series of field data and coincident high spatial resolution satellite imagery. The study area was a 142 km**2 shallow, clear water seagrass habitat (the Eastern Banks, Moreton Bay, Australia). Nine data sets acquired between 2004 and 2013 were used to create seagrass species and percentage cover maps through the integration of seagrass photo transect field data, and atmospherically and geometrically corrected high spatial resolution satellite image data (WorldView-2, IKONOS and Quickbird-2) using an object based image analysis approach. Biomass maps were derived using empirical models trained with in-situ above ground biomass data per seagrass species. Maps and summary plots identified inter- and intra-annual variation of seagrass species composition, percentage cover level and above ground biomass. The methods provide a rigorous approach for field and image data collection and pre-processing, a semi-automated approach to extract seagrass species and cover maps and assess accuracy, and the subsequent empirical modelling of seagrass biomass. The resultant maps provide a fundamental data set for understanding landscape scale seagrass dynamics in a shallow water environment. Our findings provide proof of concept for the use of time-series analysis of remotely sensed seagrass products for use in seagrass ecology and management.

Surface velocity fields, digital elevation models, ice front positions and grounding line derived from remote sensing data at Dinsmoor-Bombardier-Edgeworth glacier system, Antarctic Peninsula (1992-2014)

The northern Antarctic Peninsula is one of the fastest changing regions on Earth. The disintegration of the Larsen-A Ice Shelf in 1995 caused tributary glaciers to adjust by speeding up, surface lowering, and overall increased ice-mass discharge. In this study, we investigate the temporal variation of these changes at the Dinsmoor-Bombardier-Edgeworth glacier system by analyzing dense time series from various spaceborne and airborne Earth observation missions. Precollapse ice shelf conditions and subsequent adjustments through 2014 were covered. Our results show a response of the glacier system some months after the breakup, reaching maximum surface velocities at the glacier front of up to 8.8 m/d in 1999 and a subsequent decrease to ~1.5 m/d in 2014. Using a dense time series of interferometrically derived TanDEM-X digital elevation models and photogrammetric data, an exponential function was fitted for the decrease in surface elevation. Elevation changes in areas below 1000 m a.s.l. amounted to at least 130±15 m130±15 m between 1995 and 2014, with change rates of ~3.15 m/a between 2003 and 2008. Current change rates (2010-2014) are in the range of 1.7 m/a. Mass imbalances were computed with different scenarios of boundary conditions. The most plausible results amount to -40.7±3.9 Gt-40.7±3.9 Gt. The contribution to sea level rise was estimated to be 18.8±1.8 Gt18.8±1.8 Gt, corresponding to a 0.052±0.005 mm0.052±0.005 mm sea level equivalent, for the period 1995-2014. Our analysis and scenario considerations revealed that major uncertainties still exist due to insufficiently accurate ice-thickness information. The second largest uncertainty in the computations was the glacier surface mass balance, which is still poorly known. Our time series analysis facilitates an improved comparison with GRACE data and as input to modeling of glacio-isostatic uplift in this region. The study contributed to a better understanding of how glacier systems adjust to ice shelf disintegration.

Holocene precipitation change in different monsoon sub-regions (time-slices and transient data) simulated by different global climate models, with links to model results

The recently proposed global monsoon hypothesis interprets monsoon systems as part of one global-scale atmospheric overturning circulation, implying a connection between the regional monsoon systems and an in-phase behaviour of all northern hemispheric monsoons on annual timescales (Trenberth et al., 2000). Whether this concept can be applied to past climates and variability on longer timescales is still under debate, because the monsoon systems exhibit different regional characteristics such as different seasonality (i.e. onset, peak, and withdrawal). To investigate the interconnection of different monsoon systems during the pre-industrial Holocene, five transient global climate model simulations have been analysed with respect to the rainfall trend and variability in different sub-domains of the Afro-Asian monsoon region. Our analysis suggests that on millennial timescales with varying orbital forcing, the monsoons do not behave as a tightly connected global system. According to the models, the Indian and North African monsoons are coupled, showing similar rainfall trend and moderate correlation in rainfall variability in all models. The East Asian monsoon changes independently during the Holocene. The dissimilarities in the seasonality of the monsoon sub-systems lead to a stronger response of the North African and Indian monsoon systems to the Holocene insolation forcing than of the East Asian monsoon and affect the seasonal distribution of Holocene rainfall variations. Within the Indian and North African monsoon domain, precipitation solely changes during the summer months, showing a decreasing Holocene precipitation trend. In the East Asian monsoon region, the precipitation signal is determined by an increasing precipitation trend during spring and a decreasing precipitation change during summer, partly balancing each other. A synthesis of reconstructions and the model results do not reveal an impact of the different seasonality on the timing of the Holocene rainfall optimum in the different sub-monsoon systems. They rather indicate locally inhomogeneous rainfall changes and show, that single palaeo-records should not be used to characterise the rainfall change and monsoon evolution for entire monsoon sub-systems.