OS23F-01
A subsurface warm-eddy off Northern Baja California in July 2004
Upper-ocean eddies are commonly observed from remote sensing, but submerged eddies are more difficult to detect. During July 2004, a 21-day hydrographic survey in the southern region of the California Current was carried out to investigate the mesoscale variability. We observed for the first time a subsurface anticyclonic eddy off northern Baja California with the same water mass characteristics as the California Undercurrent. The core of the eddy was quasi-circular with radii of 35 km and thickness of 250 m. The maximum swirl velocity was ~ 3 cm/s. The water mass of the core of the eddy was characterized by potential temperature of 11ºC, salinity of 34.5, and dissolved oxygen of 1.4 ml/l. The eddy propagated westward. The subsurface warm-eddy could transport relatively saline water into the North Pacific subtropical gyre.
OS23F-02
Density ratio along an isopycnal surface in the upper ocean off Baja California
Seasonal variations of the density ratio (R) along the 25 surface potential density were studied using the
1997/2005 data of the program Investigaciones Mexicanas de la Corriente de California (IMECOCAL) off Baja
California. In particular, the effect of the El Nino 1997/1998 in the R field was examined. In order to explain the
results of the R variability, the mixed layer depth was calculated. In January and April, when the differences
between the 25 surface potential density and the mixed layer depth were < 30 m, temperature and salinity
gradients tend to be compensated (0.8 < R < 1.2). This is consistent with the theory that suggests that the
compensation mechanisms in the mixed layer are function of the horizontal density gradients. On the other hand,
in July and October, the depth of the 25 surface potential density was greater than the mixed layer depth and 1.2
< R < 1.8, furthermore, in the stronger El Nino 1997/1998 there was R > 1.8 in almost all the study area.
Results that are in agreement with the theory that suggests that the salt and heat transports are proportional to
the buoyancy in the thermocline. Termohaline fronts produced by the confluence of subartic and equatorial water
masses generated areas of compensation off Punta Eugenia.
http:www.cicese.mx
OS23F-03
Seasonal and interannual variability of barrier layer off Baja California
Seasonal and interannual variability of the isothermal layer depth (ILD) and the isopycnal layer depth (MLD) in the
southern part of the California Current are examined. The data presented were gathered during thirty one cruises
in 1997-2005 over a grid based on the Investigaciones Mexicanas de la Corriente de California (IMECOCAL)
station plan, which is the same that the CalCOFI station plan, from lines 100-130, out to station 80. The sampling
interval was 3 month. The spatial distributions of both ILD and MLD were inhomogeneous. Both the ILD/MLD
reached its maximum in January (40/60 m) and its minimum in July (15/20 m). At the first order, the MLD
variations are explained with local wind stress and surface net heat flux. The MLD was deeper than the ILD, which
means that a Barrier Layer (BL) was established. The highest BL thickness was in January (-20 m) and the
lowest in July (- 5 m). The interannual variability of the MLD was related to external forcing. As a result of the
effects of El Nino 1997-1998 in the study area, both the MLD and ILD were anomalously high (90 m), in the survey
performed in January 1998. As a result of the ENSO cycle, the BL thickness was anomalously positive (16 m), in
April 1999, and anomalously negative (- 18 m), in July 2003.
http:www.cicese.mx
OS23F-04
Comparison of Upwelling Indices Off Baja California derived from three different wind data sources
Coastal upwelling indices (i.e. offshore Ekman transport) along the western coast of North America have been produced since 1945 by the Pacific Fisheries Environmental Laboratory (PFEL), a division of the U.S. National Oceanic and Atmospheric Administration. They have been widely used for topics ranging from description of coastal circulation patterns, climate change, and linkage between environmental and biological variability. In this study, we evaluate the PFEL indices along the northern Baja California Pacific coast (27°-33°N) by comparing them with those derived from winds measured by the QuikSCAT satellite and by coastal meteorological stations. With the exception of the PFEL series off San Diego, CA (33°N), the three datasets compare reasonably well, having similar typical year patterns, correlations >0.6, and significant coherences for periods 3-5 days or longer. By contrast, the seasonal variations, the timing and magnitude of maximum upwelling, and the variability of the PFEL indices at 33°N are significantly different compared to all the other time series, including QuikSCAT at that location. Hence, caution is suggested in using the PFEL indices as estimates of upwelling in the coastal region around the U.S.-Mexico border. The performance of the QuikSCAT winds close to shore is evaluated using the coastal meteorological station data. Although large RMS errors in direction were found for the QuikSCAT winds, they reproduce well the typical year observed by the meteorological stations, and show reasonable coherences for frequencies in the weather band and lower.
OS23F-05
Effects of Climate Change on Production of Siliceous Phytoplankton Over the Twentieth Century as Recorded in Sediments of the Santa Bárbara Basin off Southern California
The relationship between production of siliceous phytoplankton and interannual through multidecadal climate variability is examined by analysis of a high-resolution paleo-record of diatoms and silicoflagellates for the period 1909-1991. The record is reconstructed from the annually layered sediments (varves) preserved in the hypoxic Santa Barbara Basin providing an annual history of production and settling to the sediments of an important fraction of the new production in the coastal environment. Location of the depositional site makes it sensitive to change in ocean climate governing large scale dynamics of the California Current ecosystem. Variables used for comparison to indices of large-scale climate change are: 1) total flux rate to the sediments of both diatom tests and silicoflagellates; 2) change in species richness; 3) the absolute and relative flux of specific functional groups (indicating conditions of upwelling and turbulence vs. stability in the water column); and 4) absolute and relative flux of a species assemblage identified as having warm water affinities. Although the combination of these variables indicates a response to interannual variability associated with ENSO, a more striking feature is the persistence over decadal and interdecadal periods exemplified by the steep decline and reduced values in the overall rate of flux after 1976 (indicating a response to the basin-scale climate shift in 1976-77). The most prominent feature, however, is a major shift in the nature of total flux, and particularly a drastic change in the relative abundances of two different species assemblages, from one that dominated through the first 30 years of the series to another that dominated through the final 40 years of the record. Although the exact nature and timing of this major transition cannot be ascertained because of a break in the record from 1944 through 1948, the change is clearly marked by the replacement of a group of small diatom species (indicative of coastal upwelling and turbulent conditions characteristic of spring and early summer) by a dissimilar assemblage of larger, more robust species (indicating warmer, more stable and oceanic conditions during late summer and fall). This transition between assemblages occurred between the late 1930s and the early 1950s and marks the change between two different states in ocean climate that appears to reflect a local response to warming along the eastern boundary of the Pacific that is a feature of the global greenhouse effect. The shift in character of the siliceous phytoplankton deposition occurred at a similar time as the change in composition of the planktonic foraminifera in the sediments at the same location, interpreted as a response to global warming by Field et al. (Science, 311: 63-66, 2006).
OS23F-06
Climate Change Impacts on Biological Production in the Arabian Sea
For the past eight years, the western half of the Arabian Sea has witnessed an almost 350 percent increase in
summer-time phytoplankton blooms due to strengthening of the southwest monsoon winds and intensification of
coastal upwelling linked to the warming trend over Eurasia. We have also observed that the warming trend is
undermining convective mixing responsible for nutrient enrichment during the boreal winter component of the
monsoon cycle, causing a decline in winter-time phytoplankton biomass in the eastern Arabian Sea. On the other
hand, the western Arabian Sea has been witnessing an increase in chlorophyll due to unprecedented blooms of
Noctiluca miliaris Suriray tied to mesoscale eddy activity and the uplift of subsurface, cooler, nutrient-rich and
oxygen poor waters seen early during the season off the coast of Oman.
http:www.bigelow.org/climatechange
OS23F-07
Generation and evolution of internal waves in Banderas Bay, Jalisco-Nayarit, Mexico.
The characteristics of internal waves in Banderas Bay (Mexico) were determined by means of data from oceanographical measurements carried on spring and winter during the years 2001 and 2003. The intense fluctuations in the fields of temperature and salinity obtained from a fast oceanographical survey with an undulating CTD on April, 2001, give evidence of the presence and propagation of an internal waves' field. With the help of a bathymetric chart elaborated from a survey carried on in March and May, 2002, we found that the submarine canyon close to the southern coast of the bay, from Cabo Corrientes to Mismaloya, acts like a filter that reflects the diurnal internal tide and allows only the entrance of semidiurnal internal tide. The results of a special experiment measuring the spatiotemporal parameters of internal waves on the wide continental shelf of northwestern Banderas Bay are discussed. The oceanographical measurements consisted of: a) a fast survey with an undulating CTD along a transect perpendicular to the coast, (b) the towing of an array of temperature and depth sensors several times over the continental shelf along transects perpendicular to the coast, and (c) time series of velocity components registered by an acoustic Doppler current profiler placed on the seabed of the bay at 28 m depth. The presence of internal waves generated by semidiurnal tide and corresponding to the second normal oscillation mode (according to the linear theory of internal waves) was determined. Analysis of the data showed that, in the study area, the internal waves generated over the continental slope by the barotropic tide have the shape of an oscillatory bore, which quickly disintegrates during their propagation shoreward, producing short nonlinear waves that dissipate close to the coast, and intense vertical mixing of the whole water column. The interpretation of the results was based on the linear and nonlinear (Korteweg-de Vries equation) theories of internal waves.
OS23F-08
The Stable Nitrogen Isotope Composition of Particulate Matter of Eastern Tropical Pacific Surface Waters During the Boreal Spring
The stable nitrogen isotope composition (15N/14N-PN relative to air N2) of surface-water particulate matter (> 0.7 μm) was measured along approximately one-degree intervals at WOCE P18 line of the Eastern Tropical Pacific Ocean between 15°S to 23°N, 103°/110°W, in April of 1994. This line intersected segments of the equatorial surface current systems (North and South Equatorial Currents, and the Equatorial Countercurrent). The δ15N-PN values in each of these features reflect N- nutrient availability to the photic zone. Near the Equator, surface waters were nitrate-sufficient (up to 6.7 μM), and δ15N-PN values were usually 0 to 5 ‰ as a result of fractionation during uptake of surplus upwelled nitrate. South of the Equator an enrichment value (ε) for nitrate uptake was calculated to be 3.8 ‰ during the depletion of equatorially-upwelled water. δ15N-PN values at the nutrient-depleted North Equatorial Current (NEC) averaged 7.2 ‰, which should resemble the isotopic composition of incoming nitrate from subsurface waters. At the NEC's northern limit, surface δ15N-PN values were isotopically enriched (16 ‰) which is consistent with the input of subsurface 15N-enriched NO3- from the oxygen minimum zone. This surface distribution is similar to that reported by others for the austral spring farther west and the Tropical North Pacific oxygen minimum zone near the Mexican coastline and suggests a constancy of processes determining the nitrogen isotopic composition of the region both in space and time.
OS23F-09
Hydrographic monitoring of El Nino 2006 of the coast of Mexico.
Hydrographic data from monthly surveys off the West Coast of Mexico (near Barra de Navidad) and time series of temperature and salinity in a mooring placed 1 km to the coast, for the period 2005-07, are analyzed. Temperature and salinity profiles of the 2006 summer-fall differ strongly from similar profiles obtained in 2005. The differences might be due to the input of large volumes of relatively warm and less saline water, with TS- characteristic suggesting a Tropical Pacific origin. By October 2006, those water masses had filled the entire 50m upper layer. The mean temperature of this water layer, in a section of 50 km from coast to open ocean, at the ending of October, 2006, was equal to 29.11 ° C, with a salinity of 33.68 psu. The mean temperature for the same section, during October, 2005, was lower than 11 ° C, and the salinity was higher than 0.95 psu. Time series of temperature, salinity and ocean level measurements at the mooring for a time interval larger than a year, since June, 2006 have shown the passage through the polygon of a long sequence of Kelvin waves with periods of about 2-3 weeks. The Kelvin waves caused a fluctuation of temperature, salinity and ocean level in the upper 50m water layer, up to 10 ° C, 0.6 psu and 20 cm, respectively. The process which caused sea surface temperature anomalies in El Nino Pacific Equatorial region B occurred one month before the temperature rises and salinity falling in the study area.
OS23F-10
Upwelling Pattern in the Gulf of Panama: an Assessment Using WOD01
While the seasonal variability of water properties in the Gulf of Panama is relatively well known, processes which rule the spatial variability are poorly understood. In view of this, we aimed to study the spatial variability of the termohaline structure of the gulf during the dry season upwelling and the rainy season using available archived data from the World Ocean Database (WOD01). For the selection of the database we considered the results from two oceanographic cruises with the largest number of sampling sites. The selected cruises were carried in November 1967 (rainy season) and in March 1933 (dry season). We used the software packages from Ocean Data View to access the WOD01, built a database, and draw the oceanographic profiles. Results have confirmed significant sea surface temperature differences between the rainy and the dry seasons (z-test = 24, p < 0.01). Warm sea surface temperature (SST > 27.5° C) and low salinity (< 31 psu) waters were commonplace during the rainy season. Colder (SST < 21° C) and more saline (> 34 psu) waters were the norm during the dry season. The mean hydrographic profile from the along-shelf transect during the dry season, showed the thermocline to be tilted toward the West side of the gulf; whereas it nearly breaks in the surface in the East side, where upwelling is more intense (SST < 20° C, salinity > 34 psu). We propose that the spatial variability of temperature and salinity in the gulf during upwelling is connected to the Ekman transport mechanism which in turn is related to wind direction and intensity. The high winds stress index (0.1 N m-2) derived from wind measurements during the March 1933 cruise point at the development of a very intense dry season upwelling.
OS23F-11
Hydrography and Current Measurements from Hawaii to western Pacific in summer 2006
Hydrographic survey and current measurements were carried out by KORDI team during the Hawaii to western Pacific Cruise between August 25 and September 30, 2006. The total study area can be classcified into three regions by the overall temperature-salinity characteristics: 1) central N. Pacific (CP) region from Hawaii to Micronesia, 2) island region near Chuuk, Micronesia (CM), and 3) northwestern Pacific (WP) region between 130oE and 135oE. Salinity maximum core is the highest (S=35.2) at the subsurface depths and the lowest (S=34.1) below the thermocline depths in CP. The range of salinity is reduced in the western Pacific; salinity maximum is up to 35.1 and the minimum is about 34.2 or higher, respectively. Near islands around Chuuk, Micronesia (CM), the upper maximum is even more reduced down to 34.8 and the lower minimum is about 34.5 and there is another salinity maximum core (S=34.65) invading into the middle of the broad depths of salinity minimum layer by the North Pacific Intermediate Water (NPIW). Consistent westward flows were measured in the upper layer by ADCP, which primarily represented the North Equatorial Currents (NEC) across the longitudes 135oE and 130oE, except near the northern tip from 18oN to 20oN at 130oE, where the currents flow in the opposite direction (eastward). The vertical structures of current profiles were also examined and compared one another, which were obtained by the lowered ADCP at the CTD stations along the cruise track in the study area. During the cruise, the SST positive anomalies at Nino 3.4 region were in a rising phase (beginning of El Nino), which had been persistently strengthening for the next winter (and still going on). The currents and hydrographic structure from the central to western Pacific regions are considered with respect to the ENSO phases in the North Pacific Ocean.
OS23F-12
On the Influence of Ocean Internal Waves on Deflections of Sea Ice Cover
The influence of ocean internal waves on the sea ice cover is a problem, which is practically important but poorly studied. It is a common assumption that the rigid lid approximation that filters out the surface mode and describes well the properties of internal waves should be valid also in the case, when the free surface is substituted by an ice cover. Since the vertical velocity at the surface is zero in the approximation, there should be no vertical displacements of the ice cover along the vertical. Thus internal waves cannot be recorded on the basis of fluctuations of the sea ice cover. Such conclusion, however, contradicts the data of observations. We have developed theoretical model, which describes propagation of internal waves in the ocean under ice cover. The sea water is considered inviscid, non-rotating, and incompressible, the Brunt-Väisälä frequency is supposed to be constant. The ice is considered of uniform thickness, with constant values of Young's modulus, Poisson's ratio, density and compressive stress in the ice. The boundary conditions are such that the normal velocity at the bottom is zero and at the undersurface of the ice the linearized kinematic and dynamical boundary conditions are satisfied. According to our results the deflections of the sea ice surface with the frequencies close but smaller than the Brunt-Väisälä frequency (i.e., with periods of tens minutes) can gain amplitudes sufficient for recording of internal waves. A comparison of the theory with observations in the Arctic Ocean showed a satisfactory agreement. This study was supported by the Russian Foundation for Basic Research (project no. 06 05-65210).