Pablo Clemente-Colón’s research while affiliated with NOAA Fisheries and other places

The contrast between the slight increase of Antarctic sea ice and the drastic reduction of Arctic sea ice since the 1970s has been a conundrum to be resolved. Sea ice trajectory tracking with satellite scatterometer data in 2008 shows that ice around Antarctica is pushed offshore by katabatic winds influenced by the continental topography. The ice trajectories reveal that sea ice, grown earlier in the ice season, drifts northward away from the Antarctic continent forming a circumpolar frontal ice zone (FIZ) behind the ice edge. The FIZ thereby consists of sea ice that becomes rougher due to a longer exposure to wind and wave actions, and thicker over time by more ice growth and greater snow accumulation. In the Antarctic circumpolar sea ice zone adjacent to the sea ice edge, satellite data in 1999–2009 exhibit a band of strong radar backscatter, which is consistent with the signature of older, thicker, and rougher sea ice with more snow in the FIZ. This sea ice band, as wide as 1000 km, serves as a ‘Great Shield,’ encapsulating and protecting younger and thinner ice in the internal ice pack. In the young and thin ice region behind the FIZ, ice can grow rapidly as winds continue opening interior areas thereby creating effective “ice factories.” In addition, ridging can enhance ice thickness by convergence toward the circumpolar FIZ that is recirculated by westerly winds and currents. During the ice growth season, the FIZ advances until reaching lower-latitude warm waters at a boundary determined by the southern Antarctic Circumpolar Current front that is constrained by seafloor features. These persistent topographical and bathymetric geological factors help sustain the Antarctic sea ice cover. As such, the behavior of Antarctic sea ice is not a paradox as some have suggested, but instead is consistent with the geophysical characteristics in the southern polar region that starkly contrast to those in the Arctic.

The Western South Atlantic Ocean is characterized by the confluence of the Brazil Current and the Malvinas (Falkland) Current, along the western margin of the Argentine Basin. The so-called Brazil-Malvinas Confluence occurs near the entrance of the La Plata River estuary, roughly between 35°S and 40°S. A significant number of papers related to different oceanographic and biological aspects of the confluence has been published with many based on thermal infrared (IR) and/or visible satellite imagery. The NOAA-AVHRR sensor, which has been most commonly used, observes this area four or five times per day in the visible and IR bands. However, this frequency is often insufficient, given the high probability of cloud cover in the region. In contrast, an active sensor such as the synthetic aperture radar (SAR) can be used day and night and under cloudy conditions to observe a variety of sea surface signatures. A GlobeSAR-2 project was carried out during 1997-1998 to monitor the confluence using ScanSAR Wide Beam Mode RADARSAT-1 images. The project aimed at determining the possibility of using these data to provide complementary information to AVHRR and defining their capability to detect ocean dynamic patterns in the region. RADARSAT-1 images were acquired during 1997 and 1998. Two 1998 images corresponding to July 19 and September 5 are presented here. Complex patterns associated with the ocean surface circulation, biological productivity, and atmospheric conditions were analyzed. The results show that under adequate wind speed conditions SAR can be used in a complementary way with NOAA-AVHRR, and provide details about different aspects of the dynamics of the region, such as fronts, filaments and eddies. The observations suggest that SAR imagery may also be able to provide a useful link between physical oceanography information derived from thermal sensors and biological information from visible sensors like Sea WiFS and MODIS.

NOAA/NESDIS a initié le programme “Alaska SAR Demonstration” dont l'objectif est de faire la démonstration du potentiel des images RSO en bande C de RADARSAT-1 à fournir une information utile et en temps opportun sur l'environnement et pour la gestion des ressources pour des utilisateurs en Alaska. Un des produits développés dans le cadre du programme est une liste de localisations des navires. Cet article décrit l'algorithme développé pour générer ce produit par le biais de la détection automatique des navires basée sur des changements dans les statistiques locales. À l'aide d'images à basse résolution (100 mètres d'espacement), on démontre que l'on peut détecter des navires de dimension supérieure à 35 mètres (représentant 105 navires sur un total de 272 dans la zone test) avec un taux de fausse alerte de 0,01% pour une seule détection. Avec des images à haute résolution (50 mètres d'espacement), on peut détecter des navires d'une dimension supérieure à 32 mètres (représentant 124 navires sur 272) avec un taux de fausse alerte de 0,002% pour une seule détection. L'algorithme est entièrement automatisé et prend environ 10 minutes de temps-machine pour traiter une image ScanSAR en mode B large.

Accentuated by a new record low in 2012, the springtime extent of Arctic perennial sea ice continues its precipitous decline. Consequently, the Arctic sea ice cover is increasingly dominated by seasonal sea ice, consisting of thinner and saltier ice with more leads (fractures), polynyas (areas of open water), nilas (sea ice crust less than about 10 centimeters thick), frost flowers (clusters of salty ice crystals on sea ice surface), and saline snow. The increase in the salinity of the sea ice cover is potentially conducive to ice-mediated photochemical and meteorological processes leading to ozone (O3) and gaseous elemental mercury depletion from the atmosphere.

The seafloor has a profound role in Arctic Sea ice formation and seasonal evolution. Ocean bathymetry controls the distribution and mixing of warm and cold waters, which may originate from different sources, thereby dictating the pattern of sea ice on the ocean surface. Sea ice dynamics, forced by surface winds, are also guided by seafloor features in preferential directions. Here, satellite mapping of sea ice together with buoy measurements are used to reveal the bathymetric control on sea ice growth and dynamics. Bathymetric effects on sea ice formation are clearly observed in the conformity between sea ice patterns and bathymetric characteristics in the peripheral seas. Beyond local features, bathymetric control appears over extensive regions of the sea ice cover across the Arctic Ocean. The large-scale conformity between bathymetry and patterns of different synoptic sea ice classes, including seasonal and perennial sea ice, is identified. An implication of the bathymetric influence is that the maximum extent of the total sea ice cover is relatively stable, as observed by scatterometer data in the decade of the 2000s, while the minimum ice extent has decreased drastically. Because of the geologic control, the sea ice cover can expand only as far as it reaches the seashore, the continental shelf break, or other pronounced bathymetric features in the peripheral seas. Since the seafloor does not change significantly for decades or centuries, sea ice patterns can be recurrent around certain bathymetric features, which, once identified, may help improve short-term forecast, seasonal outlook, and decadal prediction of the sea ice cover. Moreover, the seafloor can indirectly influence the cloud cover by its control on sea ice distribution, which differentially modulates the latent heat flux through ice covered and open water areas.

Recent drastic reduction of the older perennial sea ice in the Arctic Ocean has resulted in a vast expansion of younger and saltier seasonal sea ice. This increase in the salinity of the overall ice cover could impact tropospheric chemical processes. Springtime perennial ice extent in 2008 and 2009 broke the half-century record minimum in 2007 by about one million km2. In both years seasonal ice was dominant across the Beaufort Sea extending to the Amundsen Gulf, where significant field and satellite observations of sea ice, temperature, and atmospheric chemicals have been made. Measurements at the site of the Canadian Coast Guard Ship Amundsen ice breaker in the Amundsen Gulf showed events of increased bromine monoxide (BrO), coupled with decreases of ozone (O3) and gaseous elemental mercury (GEM), during cold periods in March 2008. The timing of the main event of BrO, O3, and GEM changes was found to be consistent with BrO observed by satellites over an extensive area around the site. Furthermore, satellite sensors detected a doubling of atmospheric BrO in a vortex associated with a spiral rising air pattern. In spring 2009, excessive and widespread bromine explosions occurred in the same region while the regional air temperature was low and the extent of perennial ice was significantly reduced compared to the case in 2008. Using satellite observations together with a Rising-Air-Parcel model, we discover a topographic control on BrO distribution such that the Alaskan North Slope and the Canadian Shield region were exposed to elevated BrO, whereas the surrounding mountains isolated the Alaskan interior from bromine intrusion.

In the decade of the 2000s, Arctic perennial (multi-year) sea ice has diminished drastically, whereas seasonal (first-year) sea ice has become the dominant ice class. This change effectively increases the overall surface salinity of the sea ice cover and in the overlying snowpack. Satellite results in 2010 and 2011 show the extent of perennial sea ice remains minimal with significant bromine explosions in the springtime. Key science questions still remain to be answered to understand the impact of the Arctic perennial sea ice reduction on low-atmospheric physical and chemical processes. Of the highest priority is to investigate the impact on bromine explosion events that lead to depletion of ozone and gaseous elementary mercury in the atmosphere. With that objective, we present the development of the BRomine, Ozone, and Mercury EXperiment in (BROMEX) in spring 2012 around Barrow, extending out to 200 km offshore and inland. In BROMEX, chemical, sea ice, snow, and ocean measurements will be made across sea ice leads both upwind and downwind areas of newly opened leads. Chemical-measurement buoys and other types of buoys will be deployed with helicopter flights to both sides of the leads. Various flight patterns of aircraft carrying ozone and bromine-measuring sensors will be used to characterize the chemical distribution over sea ice, land, and mountainous regions. Our approach will use data from multiple satellite instruments including MODIS, AMSR-E, QuikSCAT, GOME-2, SCIAMACHY, OMI, RADARSAT-2, Envisat ASAR, TerraSAR-X, TanDEM-X, SMOS, CryoSat-2 altimeter, and Oceansat-2 scatterometer. Moreover, results from recent field campaigns such as the IPY OASIS, INCATPA, CFL, SALT, and IceBridge, from sea ice and snow products generated by the U.S. Naval and National Ice Center, from NASA cryospheric observations, and from surface observation networks such as SIZONet will be utilized together with new measurements from BROMEX. Further collaborations with the international research communities related to chemistry, sea ice, snow, atmospheric processes, and biology are being arranged.

The Arctic sea ice cover has been transformed by a vast replacement of older perennial sea ice to younger seasonal ice. This rejuvenation results in an immense and relatively salty seasonal ice cover impacting chemical processes in the Arctic troposphere during the polar sun rise period. New results from the QuikSCAT satellite scatterometer (QS) show that March perennial ice extent remained low in 2010. In November 2009, the QS antenna was stuck in one azimuth direction after more than 10 years in orbit. Nevertheless, the scatterometer is still working to collect good global backscatter data although with a much reduced swath. Thus, the climatic data record of Arctic perennial ice extent in the 2000s (2000-2009) can be continued into 2010 and beyond if the QS scatterometer is kept in continuous operation, a concept we refer to as the Polar Express Mission. These measurements, in combination with those from AMSR-E radiometers, ice charts, and surface buoys, represent important complementary data to characterize the state of Arctic sea ice in the present and also in a long-term perspective. Measurements of atmospheric chemicals have been collected by satellites (e.g., OMI, GOME, GOME-2, and SCIAMACHY) and by field experiments (e.g., OASIS and CFL) and from recent deployments of O-buoys. Results show a consistency in the timing of bromine-increase episodes between satellite and field observations in March 2008. The Rising Air Parcel model reveals tropospheric patterns, under control of the regional topography, conform well to the pattern of bromine monoxide (BrO) measured by satellites. Atmospheric patterns from the low troposphere to the stratosphere are reconstructed using 3D wind fields. These results reveal the dynamic control of the wind patterns on BrO distribution in the lower troposphere, explaining the vortex and the split in the observed BrO pattern in the Beaufort Sea, while the patterns become uncorrelated in the stratosphere. Intense episodes of bromine explosions occurred in March-May in 2009 and again in 2010, when there were vast regions of seasonal sea ice and low ice surface temperature (from MODIS data). Bromine explosions with associated ozone and gaseous elementary mercury depletions can impact the atmospheric chemical and radiative balance and the rate of deposition of mercury to the Arctic Ocean surface.