Abstract:

Modeling species and community distributions over wide expanses of waters like the Southern Ocean presents strong interests for improving our understanding of marine life in remote and little-investigated areas.

 

However, available presence-only data – used to generate habitat models – often rely on the compilation of heterogeneous datasets produced from different campaigns, and might thereby introduce strong spatial (sampling strategies and areas) and temporal biases (environmental changes over the sampling period) in models. As such heterogeneities influence the performance of models, assessing their impact is critical to the relevance of modeling procedures.

 

The present study aims at testing the influence of different temporal and spatial biases in widely used modeling procedures (MaxEnt and BRT), using a dataset from the Kerguelen Plateau, for four echinoid species which display contrasted ecological niches and distribution areas. Presence-only data were compiled from different oceanographic campaigns (led over a long time period : 1872-2015) and show significant sampling heterogeneities.

 

The influence of data quantity and distribution in space and time on model performances was analyzed and compared with the influence of present and future environmental changes. BRT and MaxEnt abilities to project the models over different time periods was also tested, by comparing models based on contemporaneous data with models extrapolated from the past.

 

Results were used to model species potential shifts predicted from IPCC A1B scenarii proposed for 2100 and 2200 AD; they were compared with the magnitude of changes recorded in the past (1955-2012).

Abstract: The change of Austre Lovénbreen, a 4.5 km2 land-based glacier along the west coast of Spitsbergen, is investigated using geodetic methods and mass balance measurements over 1948–2013. For 2008−2013, annual mass balances computed on 36-stake measurements were obtained, in addition to annual mass balances reconstructed from the neighbouring glaciers, Midtre Lovénbreen (1968−2007) and Austre Brøggerbreen (1963−1967). The mean rate of glacier retreat for 1948–2013 is −16.7 ± 0.3 m a−1. Fluctuations in area (1948–2013 mean, −0.027 ± 0.002 km2 a−1) showed a slowing as the glacier recedes within its valley from 1990 to 1995. For 1962–2013, the average volume loss calculated by digital elevation model subtraction of −0.441 ± 0.062 m w.e. a−1 (or −0.54 ± 0.07% a−1) is similar to the average annual mass balance (−0.451 ± 0.007 m w.e. a−1), demonstrating a good agreement between the loss rates computed by both methods over 1962−2013. When divided in two periods (1962−1995 and 1995−2013), an increase in the rate of ice mass loss is statistically significant for the glacier volume change. The 0°C isotherm elevation (based on mean May–September air temperatures) is estimated to have risen by about 250 m up to the upper parts of the glacier between 1948 and 2013. The glacier area exposed to melting during May to September almost increased by 1.8-fold while the area reduced by a third since 1948. Within a few years, the glacier area exposed to melting will decrease, leading the upper glacier parts under the 0°C isotherm while the snout will keep on retreating.

Abstract: Taking the 32 storm sudden commencements (SSCs) listed by the International Service of Geomagnetic Indices (ISGI) of the Observatory de l’Ebre during 2002 (solar activity maximum in Cycle 23) as a starting point, we performed a multi-criterion analysis based on observations (propagation time, velocity comparisons, sense of the magnetic field rotation, radio waves) to associate them with solar sources, identified their effects in the interplanetary medium, and looked at the response of the terrestrial ionized and neutral environment. We find that 28 SSCs can be related to 44 coronal mass ejections (CMEs), 15 with a unique CME and 13 with a series of multiple CMEs, among which 19 (68%) involved halo CMEs. Twelve of the 19 fastest CMEs with speeds greater than 1000 km s−1 are halo CMEs. For the 44 CMEs, including 21 halo CMEs, the corresponding X-ray flare classes are: 3 X-class, 19 M-class, and 22 C-class flares. The probability for an SSC to occur is 75% if the CME is a halo CME. Among the 500, or even more, front-side, non-halo CMEs recorded in 2002, only 23 could be the source of an SSC, i.e. 5%. The complex interactions between two (or more) CMEs and the modification of their trajectories have been examined using joint white-light and multiple-wavelength radio observations. The detection of long-lasting type IV bursts observed at metric–hectometric wavelengths is a very useful criterion for the CME–SSC events association. The events associated with the most depressed Dst values are also associated with type IV radio bursts. The four SSCs associated with a single shock at L1 correspond to four radio events exhibiting characteristics different from type IV radio bursts. The solar-wind structures at L1 after the 32 SSCs are 12 magnetic clouds (MCs), 6 interplanetary coronal mass ejections (ICMEs) without an MC structure, 4 miscellaneous structures, which cannot unambiguously be classified as ICMEs, 5 corotating or stream interaction regions (CIRs/SIRs), one CIR caused two SSCs, and 4 shock events; note than one CIR caused two SSCs. The 11 MCs listed in 3 or more MC catalogs covering the year 2002 are associated with SSCs. For the three most intense geomagnetic storms (based on Dst minima) related to MCs, we note two sudden increases of the Dst, at the arrival of the sheath and the arrival of the MC itself. In terms of geoeffectiveness, the relation between the CME speed and the magnetic-storm intensity, as characterized using the Dst magnetic index, is very complex, but generally CMEs with velocities at the Sun larger than 1000 km s−1 have larger probabilities to trigger moderate or intense storms. The most geoeffective events are MCs, since 92% of them trigger moderate or intense storms, followed by ICMEs (33%). At best, CIRs/SIRs only cause weak storms. We show that these geoeffective events (ICMEs or MCs) trigger an increased and combined auroral kilometric radiation (AKR) and non-thermal continuum (NTC) wave activity in the magnetosphere, an enhanced convection in the ionosphere, and a stronger response in the thermosphere. However, this trend does not appear clearly in the coupling functions, which exhibit relatively weak correlations between the solar-wind energy input and the amplitude of various geomagnetic indices, whereas the role of the southward component of the solar-wind magnetic field is confirmed. Some saturation appears for Dst values <−100<−100< -100 nT on the integrated values of the polar and auroral indices.