Hurricanes Emily, Stan and Wilma made landfall along the Yucatan Peninsula (YP) in 2005 impacting regional coastal
environments. The effects of these hurricanes on the coastal and oceanic waters around the YP were examined using
multiple satellite sensor data such as winds from QuikSCAT, sea surface temperature (SST) from MODIS, and biooptical
properties from the SeaWiFS ocean color sensor. QuikSCAT wind data revealed the hurricane paths along with
typical changes in wind speed and direction and improved interpretation of the SST and ocean color data. SST imagery
before and after hurricanes landfalling indicated variable extent of upper ocean cooling that varied with the hurricane
track and its intensity. An examination of SeaWiFS-derived backscattering coefficient at 443 nm, an optical indicator of
suspended particulate matter concentrations showed elevated levels of surface suspended material following the hurricane passages in both nearshore and offshore waters, likely due to resuspension and offshore transport. The use of multi-satellite data provided a greater understanding of the response and changes in sea surface properties to hurricanes in the YP.
Particulate absorption (aP()) including phytoplankton (aPHY()) and non-algal particles (NAP) (aNAP()) were measured in southeastern Bering Sea during a cruise in July 2008. This study analyzes the aP() properties through in-situ and quasi analytical algorithm (QAA) derived ocean color satellite Medium Resolution Imaging spectrometer (MERIS) and Moderate resolution Imaging Spectroradiometer (MODIS) observations. We found that the aP() and aPHY() correlated well with chlorophyll-a and were lower as a function of chlorophyll-a as compared to low latitudes. The specific phytoplankton absorption (a*PHY()) showed more variability in the blue as compared to the red part of the spectrum indicating pigment packaging and/or change in pigment composition. The remote sensing reflectance (Rrs()) showed significant variability in spectral shape and magnitude which was consistent with the variable total absorption minus pure water absorption (aT-W()) spectra observed in the study area. Simple satellite retrieved Rrs() ratios were related to in-situ aPHY() and aDG() by applying an inverse power fit; Rrs(490)/Rrs(510) gave the best results for aPHY(443) and aDG(443) (R2 - 0.80 and 0.75) respectively. The match-ups of in-situ and MERIS retrieved aPHY() and NAP plus colored dissolved organic matter (aDG()) using QAA after log-transformation showed reasonable agreement with R2 of 0.71 and 0.61 and RMSE of 0.316 and 0.391 at 443 nm, respectively. Although the QAA derived aPHY() and aDG() from MERIS overestimated and underestimated, respectively the in-situ measurements at all wavelengths, the match-up analysis was encouraging.
°Empirical orthogonal function (EOF) analysis was used to study spatio-temporal variability of the Moderate Resolution
Imaging Spectroradiometer (MODIS) imagery of sea surface temperature (SST (C)) and chlorophyll (mg m-3) for the
eastern Bering Sea for May, June, July, August, September (MJJAS) for a period of 7 years (2003 - 2009). The EOF
analysis was conducted on SST and chlorophyll monthly composites that were normalized by subtracting the spatial and
temporal means with cloud, ice and land cover masked out. The SST in eastern Bering Sea showed a transition from a
warm period (2003-2005) to cooler period (2006-2009). The first 3 EOF modes of SST were retained as they explained
76.7% of the spatio-temporal variability, with the first SST EOF mode explaining 59.5% of the total variation of SST in
the study area during the study period. For the chlorophyll dataset, the first 3 EOF modes explained greater than 58.5%
of the spatio-temporal variability, with the first chlorophyll EOF explaining 28.14% of total variance in chlorophyll. The
decreasing amplitude of first SST EOF and switching from mostly positive to negative amplitude of the third chlorophyll
EOF mode in 2006 was consistent with the May SST Index, Ice Cover Index and Bering Sea Pressure Index (BSPI).
Short-term and seasonal estimates of colored dissolved organic matter (CDOM) absorption at 412 nm and
surface salinity were derived from the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) satellite data for
the Louisiana-Texas coast during 2005 using an empirical CDOM algorithm and a conservative CDOMsalinity
relationship. Field measurements obtained during various seasons in 2005 indicated high
correlations between field and satellite estimates of CDOM suggesting satellite estimates to be good
representation of the surface CDOM and salinity fields. Discharge from the Mississippi and Atchafalaya
rivers strongly influenced the seasonal surface CDOM distribution as well as during a frontal passage.
Clear satellite imagery obtained before and after the passage of a cold front in March 2005 indicated a general decrease in surface CDOM and an offshore increase of elevated CDOM suggesting that frequent frontal passages contribute to mixing of riverine CDOM and its offshore transport. A comparison of SeaWiFS-derived salinity with the salinity outputs of a three-dimensional Navy Coastal Ocean Model (NCOM) indicated similar salinity trends offshore and a region of freshwater influence along the inner shelf. Following the frontal passage, changes in the surface salinity were observed mainly closer to the coast with a general increase in mid-shelf waters, likely due to mixing of lower salinity surface waters with higher salinity sub-surface waters. Short-term salinity model simulation could be improved with daily assimilation of river discharge data. SeaWiFS derived seasonal salinity estimates provided a synoptic view of the effects of coastal circulation and riverine discharge on shelf variability.
Measurements of particulate absorption, namely absorption by phytoplankton and non-algal particles (NAP) are
important components in bio-optical models; only a few studies have been reported for the southeastern Bering Sea. This
study analyzes variability in spectral particulate absorption (aP(λ)) including phytoplankton (aPHY(λ)) and NAP
absorption (aNAP(λ)) from in-situ data in conjunction with ocean color satellite data (MODIS - Moderate Resolution
Imaging Spectroradiometer) along four transects in the southeastern Bering Sea shelf during a cruise in July 2008.
Results obtained indicate that surface aPHY(λ) at 443 nm is higher in middle shelf near the Pribilof Islands with aNAP(λ)
decreasing from north to south across the shelf. Greater than 90% of variability in aP(λ) could be explained by aPHY(λ)
indicating biogenic matter dominates changes in particulate absorption. Good correlations were found between aP(λ),
aPHY(λ) at 443 nm and chlorophyll-a (R2 = 0.65 and 0.80, respectively). aPHY(λ) spectra were highly variable, with larger
variability in blue than red part of the spectrum, indicating change in pigment composition or package effect. MODIS
satellite derived aPHY(λ) using quasi-analytical algorithms (QAA) revealed patterns similar to in-situ absorption data for a
major part of the study area. Inconsistencies seen between in-situ absorption and QAA retrieved satellite absorption
could probably be attributed to temporal differences between in-situ data collection and satellite overpass.
KEYWORDS: Satellites, Magnesium, Data centers, Solar radiation, Temperature metrology, Scanning probe microscopy, Absorption, Data archive systems, Data conversion, Spatial resolution
QuikSCAT satellite based vector wind data were used to examine wind influence on SeaWiFS derived chlorophyll a
(chlorophyll) surface distribution in the northern Gulf of Mexico waters influenced by the Mississippi and
Atchafalaya Rivers, the largest in North America. Short-term satellite derived wind field revealed a systematic shift
in direction and amplitude of the winds during a cold front passage in March 2002 that strongly influenced the
surface chlorophyll distribution. Both the offshore extent and westward transport of enhanced surface chlorophyll
biomass increased following the frontal passage. Monthly surface wind stress derived from the 12.5 km high
resolution QuikSCAT winds mapped along with SeaWiFS derived surface chlorophyll during a low flow and a
normal river discharge year in 2000 and 2001 indicated the dominant role of river discharge in influencing the
concentration and extent of chlorophyll in the plume and inner shelf waters. However the magnitude and direction of
wind stress strongly influenced the plume orientation and the cross-shelf extent of a coastal band of elevated
chlorophyll. Wind stress also influenced the offshore cross-shelf variability in surface chlorophyll distribution.
The optical properties of colored dissolved organic matter (CDOM) were studied for the northern Gulf of
Mexico coastal and oceanic waters influenced by the Mississippi-Atchafalaya river system. CDOM
absorption determined from field measurements in March, May, July and August of 2005 at a station off
the Atchafalaya river indicated influences related to river discharge while the CDOM spectral slope S
indicated effects of CDOM photooxidation in a sample acquired in late summer. A previously derived
CDOM algorithm using the reflectance band ratios of Rrs(510)/Rrs(555) were used to derive estimates of
surface CDOM absorption distribution at 412 nm from the Sea-viewing Wide Field-of-view Sensor
(SeaWiFS) imagery. Spatial and temporal CDOM absorption distributions from satellite for the northern
Gulf of Mexico in the year 2005 indicated strong seasonal influence associated with discharge from the
Mississippi-Atchafalaya river system. A seasonal increase in storms and hurricanes allowed an assessment
of the effects of hurricane Rita in September 2005. SeaWiFS estimates of CDOM revealed a decrease in
nearshore CDOM absorption due to the transport of low CDOM offshore waters towards the coast
following hurricane Rita. Using conservative CDOM-salinity relationship for the region, SeaWiFS surface
salinity derived from CDOM absorption also indicated an increase in nearshore salinity east of the
hurricane track. However, an increase in CDOM and a decrease in salinity were observed in coastal waters
near the location of hurricane landfall likely associated with coastal runoff following extensive coastal flooding.
The coastal region comprising the states of Louisiana, Mississippi, and Texas is frequently impacted by
meteorological events such as frontal passages and hurricanes. The region is also influenced by the
Mississippi river, which is seventh largest in terms of water and sediment discharge among the major rivers
of the world that strongly influences the physical and biogeochemical properties in the northern Gulf of
Mexico. NASA remote sensing data such as winds from QuikSCAT, sea surface height anomaly (SSHA)
from Jason-1, ocean color and sea surface temperature (SST) from MODIS satellite sensors were assessed
during the period that Hurricane Rita made landfall on 24 September 2005 along the Louisiana-Texas
border in the western Gulf of Mexico. QuikSCAT winds revealed the northwestward movement of the
hurricane and gradients in the distribution of wind speed around the hurricane center. Altimeter data
indicated changes in pattern of the SSH anomaly field and a displacement of the warm and cold core eddies
following the hurricane. Although limited by cloud cover, the MODIS 8-day average chlorophyll imagery
obtained before and after the hurricane indicated an offshore displacement of higher chlorophyll
concentrations while the MODIS 250 m resolution true color imagery showed high levels of suspended
particulate matter in the impacted coastal region. MODIS SST indicated a cooling of the surface waters
around and east of the track following Hurricane Rita. The use of multiple remote sensing products
provided better insights of the oceanographic response to Hurricane Rita.
Colored dissolved organic matter (CDOM) optical properties were studied in the northern Gulf of Mexico coastal waters influenced by the Atchafalaya River in July 2005 during a period of low river discharge using both field and satellite ocean color data. Although a general conservative CDOM absorption-salinity relationship between the riverine and oceanic end members were observed, deviations in surface CDOM absorption from this relationship (CDOM loss) and average higher spectral slope S of the log-linearized absorption spectra in comparison to bottom waters suggested photodegradation of surface CDOM. Excess CDOM absorption in bottom waters at many stations were associated with low oxygen or hypoxic conditions suggesting a potential CDOM source due to remineralization of organic matter in the bottom waters. At a few stations anomalously high CDOM absorption could be linked to biological production associated with algal blooms. Absorption spectra of a surface sample at one such station deviated from standard exponential form in the 300-400m UV range probably due to the presence of photo-protective pigments. CDOM derived from the Sea-Viewing Wide Field-of-View Sensor (SeaWiFS) using a regional algorithm provided a synoptic view of surface CDOM variations and the extent of river influences into the northern Gulf of Mexico.
A prototype in situ multi-sensor fiber optic fluorometer is described which was designed to acquire long term time-series fluorescence measurements. The multi-sensor system uses dual detectors with four excitation sources, thereby providing for independent measurements at eight sensor locations. Strobe excitation light of wavelength < 500 nm is passed through one of each pair of optical fibers and stimulated chlorophyll fluorescence is carried back to a photomultiplier tube. The excitation and detection hardware are enclosed in a pressure case along with a battery operated 500 kHz data acquisition/storage system. Aspects of the design of the fiber optic sensor are described which were intended to optimize detection of fluorescence signals and minimize interference by ambient light. An illustration of the utility of fiber optics for fluorescence measurements was made by comparing a prototype fiber optic profiling fluorometer with a commercial fluorometer. Time series fluorescence measurements were made with the multi-sensor fluorometer in the Gulf of Mexico, and revealed chlorophyll variability in the benthic boundary layer.
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