Gulf Stream Warm-core Ring Research Articles

GENERIC CHARACTERIZATION OFACTINOCYCLUS:CONSIDERATION IN LIGHT OF THREE NEW SPECIES

Three new species of Actinocyclus are described: A. circellus, from the Gulf of Mexico and North Atlantic (in Gulf Stream warm core rings); A. vestigulus, also from warm core rings; and A. spiritus, from antarctic waters. The morphology of these species provides insights into the generic characterization and evolution of Actinocyclus. The taxononomic preeminence of the pseudonodulus is challenged; a morphological continuum supports the suggestion that the pseudonodulus formed from a fusion of several marginal areolae. A possible rudimentary labiate process is shown near the centre of a forming valve of A. vestigulus, suggesting that Actinocyclus at least shares a common ancestor with Azpeitia. Segmented bands were seen on the largest of the three species, A. circellus.

Grazer control of the fine-scale distribution of phytoplankton in warm-core Gulf Stream rings

Grazer control of the fine-scale distribution of phytoplankton in warm-core Gulf Stream rings

Lateral exchange within Gulf Stream warm-core ring surface layers

The radial exchange of near-surface properties in Gulf Stream anticyclonic, warm-core rings is studied with the use of hydrographic and satellite data in coordination with some simple models. Analysis of physical data is restricted to the salinity field because it is the most conservative property available in the near-surface ring. A calculation of the azimuthal averaged salinity as a function of radius from ring center for cruises in April and June 1982 in ring 82B gives lower bounds on the lateral exchange in the ring of 1.07 × 10 7 kg s −1. The exchange rate reaches a maximum just inside the location of maximum surface velocities at a radius of 40 km. Similar rates of exchange can be deduced from earlier data taken in ring 81D. This inward flux of low salinity Slope Water enhances the near-surface stratification. Such a transport of fluid can be more important than surface heating in the determination of the near-surface stability except in very strong winter storms. Horizontal transport of fluid into the ring can be explained by a horizontal diffusivity of ≈ 90 m 2 s −1 if adjective effects are ignored. Adjective terms make the actual strength of diffusion uncertain. Shear dispersion or inward radial advection can reduce the necessary diffusivity while an outward radial flow would demand higher diffusivities. The importance of lateral exchange to biological properties is examined with a simple model where the ring, its surrounding frontal zone, and the far field Slope Water make up three interacting components. If the ring frontal zone is assumed to have higher “production”, either due to increased vertical mixing or through active concentration of organisms tied to convergence, the core of the ring can eventually exceed the far field Slope Water concentrations. Edge enhancement in the ring frontal zone is consistent with a time series of Coastal Zone Colour Scanner (CZCS) chlorophyll images over the April–June 1982 period as well as other observations in ring 82B.

Satellite infrared observations of Kuroshio warm-core rings and their application to study of Pacific saury migration

Satellite infrared observations of Kuroshio warm-core rings (KWCRs), made in the Tohoku area west of 150°E from February 1980 to June 1981, were used to study the effect of ring distributions on the migration routes of the epi-pelagic and migratory fish Pacific saury. Cololabis saira (Brevoort). The movement and mean speed of three KWCRs and a Tsugaru warm current gyre were determined in the study area. KWCRs tended to drift to the north or to the east at a mean speed of 5 cm s −1. This drift speed is similar to that of Gulf Stream warm-core rings, but the drift direction is quite different from the westward drift in the Gulf Stream system. A comparison between distribution of KWCRs and distribution of fish schools suggests that the KWCRs control southward migration routes of Pacific saury through interaction with the surrounding cold waters such as the First and Second Oyashio Intrusions. Satellite infrared monitoring of KWCRs and the surrounding cold waters have proved to be useful for the short period prediction of Pacific saury fishing ground formation.

Gulf Stream warm rings: a statistical study of their behavior

A 10 year series of NOAA polar-orbiter satellite infrared-based determinations of Gulf Stream warm-core ring (WCR) locations, is used to derive mean loci, lifetime and size, and movement statistics in the Slope water region off the northeast United States east coast. This time series, produced by the NOAA/NMFS Atlantic Environmental Group, is validated against precision observations of WCR frontal loci by investigators at the Universities of Miami and Rhode Island: an r.m.s. error of ± 15 km in latitude and longitude between the two sets is determined. We find that the ensemble of WCR lifetime is bi-modal with the split at 140 days. Rings are formed with a semi-major axis of ≈75 km. Longer-lived rings show a reduction in size over their lifetime to ≈35 km, shorter-lived rings do not. Ring movement shows some dependence on location, but mean motions are never <1.6 cm s −1; averaged translation speed is 6.5 cm s −1. Longer-lived rings tend to be located farther away from the climatological Gulf Stream north wall than shorter-lived rings east of 66°W. The mean loci are compared with Warm Core Ring Experiment results for 82B. We find similar changes in track corresponding to topographic variation, similar translation speed, size, decrease in size over time, etc., leading us to conclude that the kinematics observed for 82B are representative of those for a long-lived warm-core ring.

Convectively Driven Turbulent Mixing in the Upper Ocean

Abstract Two experiments were performed to study the characteristics of turbulence in convective mixed layers in the upper Ocean. In the first, a diurnal convective mixed layer developed in the Bahamas under the influence of the cycle of daytime solar heating and nighttime evaporative cooling. The mixed layer reached as deep as 100 m each night and restratified each day. In the second, the mixed layer of a warm-core Gulf Stream ring deepened from less than 50 m to more than 150 m in a little more than a day, when subjected to rapid cooling during a cold air outbreak. Although individual profiles of ϵ, the rate of viscous dissipation of turbulent kinetic energy, had considerable spatial and temporal variability, the mean dissipation profiles were similar to those in convecting atmospheric boundary layers. The ¯ϵ is established by the surface buoyancy flux, Jb0;ϵ/Jb0 = 0.61 and 0.72 in the Bahamas and ring data, respectively, compared with 0.64 in convecting atmospheric mixed layers. The mean profiles decre...

Biomass of the micronekton in Gulf Stream ring 82-B and environs: changes with time

Micronekton biomass was sampled in warm-core Gulf Stream ring 82-B (at ages 2, 4 and 6 months), the Slope Water, the Gulf Stream and the Sargasso Sea during three multi-ship cruises. There was no significant diel difference in the 0–1000 m integrated biomass for fishes or invertebrate micronekton in 24 paired day-night tows, and no evidence for diel vertical migration across the 1000 m level. Biomass showed a consistent upward shift at night; although it varied with hydrographic regime and sampling date, median biomass depth shift for invertebrates averaged 184 and 137 m for fishes. For total micronekton, median biomass depth ranged from 550 to 750 m by day and 300 to 600 m by night. Fish biomass was always centered deeper than 250 m, while the center of invertebrate biomass rose above that level in only one of 12 night tows. In April, ring-core biomass for fishes and invertebrates (2.2 and 11.9 cc m −2, respectively) was significantly lower than that for the high velocity region (3.6 and 19.8 cc m −2) or that for the Slope Water (4.7 and 20.8 cc m −2). By June, ring-core standing stocks had doubled while that for the high velocity region had been reduced to half of the April levels. No significant changes in Slope Water biomass occurred over the April–August period. Fluctuations in ring-core micronekton biomass were probably due to both in situ processes and advective exchange. On the average, invertebrate biomass was about 4 times that of fish biomass. Total micronekton was 20–30% of the macrozooplankton biomass in April and June, and 7–16% in August. Vertically, the invertebrate fraction overlapped the macrozooplankton more than did the fish fraction. Greater overlap of micronekton and macrozooplankton occurred at night.

Bacterial biomass in warm-core Gulf Stream ring 82-B: mesoscale distributions, temporal changes and production

The distribution of bacterioplankton biomass and productivity in warm-core Gulf Stream ring 82-B generally corresponded to the physical and dynamical structure of the ring. Mean cell volumes were uniform for 4 months, but were larger by a factor of 2–3 in the high velocity (frontal) region (HVR) near the ring edge. As a result of this gradient and higher abundances, water column biomass and production were highest in the front, which appeared to be a local maximum in those properties. In this regard bacterioplankton contrasted strongly to phytoplankton, which exhibited strong local maxima at the center of the ring in June. In April when the water column inside the ring was isothermal to 450 m, bacterial biomass and production were low and uniform to 250 and 50 m, respectively. Bacterioplankton responded dramatically to the vernal restratification of the ring. In June when the surface layer was characterized by a strong pycnocline at 10–40 m, bacterial biomass and production often had strong subsurface maxima, and were 3 and 5 times greater than in April, respectively. Abundance exceeded 1.5 × 10 9 cells l −1 at ring center and exceeded 3 × 10 9 l −1 in the HVR. Turnover rates for the euphotic zone bacterioplankton as a whole were 0.24 d −1 in April, 0.56 d −1 in June, and 0.27 d −1 in August at ring center. Bacterial production averaged 12% of hourly primary production (range 1–32%), suggesting that bacteria control a significant and sometimes large portion of the carbon cycling in the euphotic zone. These data suggest that warm-core rings are sites of enhanced variability of bacterioplankton properties in the open sea. Furthermore, the data strongly support recent work showing that frontal zones are sites of locally enhanced bacterial biomass and production. In the ring system as a whole, the euphotic zone bacterioplankton biomass and production were comparable to and occasionally greater than the biomass and production of the >64 μm zooplankton, especially in the HVR. Bacterioplankton appear to carry out a major fraction of the heterotrophic carbon cycling in oceanic frontal regions.

Multivariate statistics applied to phytoplankton data from two Gulf Stream warm core rings1

Multivariate statistical techniques were used on data from two cruises to Gulf Stream warm core rings to reveal patterns and relationships between phytoplankton species abundance and environmental parameters. Principal component analysis (PCA) was performed on each cruise separately and on the combined data to help delineate groups of stations, depths, and species. A ring center station with high numbers of diatoms and a Slope Water station formed separate groups. Deep samples from all the stations grouped together. We consistently observed strong similarities in phytoplankton abundance and species composition between fall samples from the two rings. Inverse analysis was performed using presence or absence data, and the values of the first three principal components were then used in a cluster analysis to determine species co‐occurrences. This analysis resulted in separate groupings of a large number of diatom species found at the center of the rings, of deep species, and of the most abundant and the most frequently observed taxa.Simple correlations, multiple regressions, and canonical correlations were performed with the phytoplankton log abundance data and the environmental data. The canonical coefficients and correlations suggest that high numbers of dinoflagellates and other algae are associated with lower salinity in the Slope Water and at the ring edge, and that higher temperatures and low values of silica (dissolved) are reflected in higher numbers of diatoms and coccolithophorids at ring center.

Velocity Profiles in a Warm-Core Ring

A transect of velocity profiles across Gulf Stream warm-core ring 82-B shows that the thermostad contained virtually no vertical shear. Enhanced downward-propagating near-inertial wave shear was present at the base of the core, consistent with these waves encountering critical layers as they try to leave the region of negative vorticity. Wave amplification and a shrinking vertical wavelength at the critical layer should lead to instability and shear production of turbulence. High dissipation rates have been observed at the base of ring 81-D's core.

Seabird Patchiness in Tropical Oceanic Waters: The Influence of Sargassum “Reefs”

Abstract The relationships of seabirds to the holopelagic macroalga Sargassum were studied during a 2-yr survey in the South Atlantic Bight off the southeastern United States. Seabirds were significantly more abundant in waters with large (&gt;5 m2) patches of the alga, and mean avian density was 32-43 times greater in waters where Sargassum was present than in adjacent waters without the alga. Seabirds aggregate at Sargassum patches formed by Langmuir circulation, convergence fronts, Gulf Stream eddies, and Gulf Stream warm core rings. Twenty-three seabird species foraged at Sargassum. Significantly more than 50% of White-tailed Tropicbirds (Phaethon lepturus), Masked Boobies (Sula dactylatra), and Bridled Terns (Sterna anaethetus) were observed at algal patches. Species that use aerial-dipping and plunge-diving foraging behaviors displayed the greatest affinity for Sargassum. Large-bodied seabirds (large shearwaters, tropicbirds, and boobies) generally were found at large patches, while small-bodied species (phalaropes and Puffinus lherminieri) occurred at smaller patches. The seasonal abundance of the pelagic Bridled Tern corresponded to seasonal variation in Sargassum abundance. Most seabirds associated with Sargassum for foraging, but Bridled and Black terns (Chlidonias niger) also used large algal mats for roost sites. The highly localized biomass of the pelagic Sargassum community and its associated motile macrofauna (zooplankton and fish) may allow seabirds to forage efficiently for prey in the oligotrophic surface waters of tropical marine environments. The patchy occurrence of Sargassum "reefs" may explain part of the local and mesoscale variation in seabird distribution and abundance in portions of the western North Atlantic Ocean.

The Diatom Genus Thalassiosira Cleve in Gulf Stream Warm Core Rings: Taxonomy, with T. intrannula and T. lineoides, spp. nov.

The Diatom Genus <i>Thalassiosira </i>Cleve in Gulf Stream Warm Core Rings: Taxonomy, with <i>T. intrannula </i>and <i>T. lineoides, </i>spp. nov.

Gulf Stream warm-core rings : Joyce, T.M. et al., 1985. Special section. J. geophys. Res., 90(C5): 8801–8951; 13 papers

Gulf Stream warm-core rings : Joyce, T.M. et al., 1985. Special section. J. geophys. Res., 90(C5): 8801–8951; 13 papers

Macrozooplankton biomass in Gulf Stream warm-core rings: spatial distribution and temporal changes : Wiebe, P.H., G.R. Flierl, C.S. Davis, Valerie Barber and S.H. Boyd, 1985. J. geophys. Res., 90(C5):8885–8901

Macrozooplankton biomass in Gulf Stream warm-core rings: spatial distribution and temporal changes : Wiebe, P.H., G.R. Flierl, C.S. Davis, Valerie Barber and S.H. Boyd, 1985. J. geophys. Res., 90(C5):8885–8901

Macrozooplankton biomass in a warm-core Gulf Stream ring: time series change in size structure, taxonomic composition, and vertical distribution : Davis, C.S. and P.H. Wiebe, 1985. J. geophys. Res., 90(C5):8871–8884.

Macrozooplankton biomass in a warm-core Gulf Stream ring: time series change in size structure, taxonomic composition, and vertical distribution : Davis, C.S. and P.H. Wiebe, 1985. J. geophys. Res., 90(C5):8871–8884.

Upper-ocean velocity structure of Gulf Stream warm-core ring 82B : Joyce, T.M. and M.A. Kennelly, 1985. J. geophys. Res., 90(C5):8839–8844

Upper-ocean velocity structure of Gulf Stream warm-core ring 82B : Joyce, T.M. and M.A. Kennelly, 1985. J. geophys. Res., 90(C5):8839–8844

Spatial and temporal patterns in pigment biomass in Gulf Stream warm-core ring 82B and its environs : Smith, R.C. and K.S. Baker, 1985. J. geophys. Res., 90(C5):8859–8870

Spatial and temporal patterns in pigment biomass in Gulf Stream warm-core ring 82B and its environs : Smith, R.C. and K.S. Baker, 1985. J. geophys. Res., 90(C5):8859–8870

Small-scale cyclones on the periphery of a Gulf Stream warm-core ring : Kennelly, M.A., R.H. Evans and T.M. Joyce, 1985. J. geophys. Res., 90(C5): 8845–8857

Small-scale cyclones on the periphery of a Gulf Stream warm-core ring : Kennelly, M.A., R.H. Evans and T.M. Joyce, 1985. J. geophys. Res., 90(C5): 8845–8857

Distribution and composition of biogenic particulate matter in a Gulf Stream warm-core ring

We have characterized the biogenic particle field in Gulf Stream warm-core ring 82-B in June of 1982. Our observations include chlorophyll α and phaeopigments, ATP, particulate organic carbon and nitrogen, biogenic silica, total particle volume and size distribution, bacterial abundance and picoplankton biomass, and the abundances of diatoms, dinoflagellates and coccolithophorids in the upper 700 m along two transects of the ring. A distinct maximum in phytoplankton biomass occurred within the thermocline (20 to 40 m) at the ring's center of rotation. This maximum had not been present in late April, and apparently developed within 3 to 4 weeks after the ring stratified in mid May. It exhibited a high degree of axial symmetry about the center of the ring, with biomass decreasing outward from ring center. A second biomass maximum associated with shelf surface water was being entrained into the anticyclonic flow field of the ring 60 to 70 km from its center. Maximum chlorophyll α and ATP concentrations observed in the two biomass maxima were similar, but the ring-center maximum was 2 to 10 times richer in particulate carbon, biogenic silica, particles > 5 μm in diameter, dinoflagellates, diatoms and estimated organic detritus, while the entrained shelf water had 2 to 5 times greater abundances of unicellular monads. Heterotrophic bacterial abundance and biomass, and the abundance of cocoid cyanobacteria were maximal in the region of highest rotational velocity 40 to 50 km from ring center. In this region the abundances of bacteria and cyanobacteria were 2 to 5 times as great as at the center of the ring. Two possible mechanisms can explain the development of an axially symmetrical maximum in biogenic particulate matter in the center of a warm-core ring: concentration by the flow field and in situ growth. Our data on the distribution and composition of biogenic material in ring 82-B indicate a greater likehood that this particular ring-center maximum developed in situ.

Seasonal variations in the phytoplankton biomass and productivity of a warm-core Gulf Stream ring

Phytoplankton biomass, as chlorophyll a (Chl a) and ATP, and carbon productivity rates were determined in three cruises to a warm-core Gulf Stream ring. Ring 82B was formed in late February 1982 with observations made in April to May, June and August. Vertical profiles of Chl a, ATP and particulate organic carbon (POC) in April to May showed little vertical structure during a period when the ring mixed layer extended from the surface to >350 m . Daily productivity rates, Chl a and ATP biomass estimates of the euphotic zone were similar to those in the source waters, the Sargasso Sea, but lower than those in contiguous Slope Waters. Despite the absence of a stratified surface layer in the ring, the phytoplankton productivity rates, assimilation numbers, and carbon-specific growth rates were relatively high. In June, a pycnocline existed at 25 m across the ring with biomass maxima of Chl a, ATP, and POC occurring near the seasonal pycnocline. Although the range in productivity in June (0.26 to 0.98 gC m −2 day −1) was similar to that in April, the carbon biomass estimated from ATP increased from 1.42 to 4.77 gC m −2 between the two cruises. The increase was partially attributed to an increased heterotrophic biomass. Carbon-specific specific doubling times in June were, most likely, influenced by the presence of a large heterotrophic ATP component. In August the surface layer of the ring was displaced by intrusions, or overwash, of Slope and Gulf Stream waters. During the 6 month lifespan of 82B total primary production was estimated at 126 gC m −2, a value similar to productivity estimates for the contiguous Slope Waters.