Candela et al. [2003] have reported empirical orthogonal function (EOF) analyses based on 23-mont... more Candela et al. [2003] have reported empirical orthogonal function (EOF) analyses based on 23-month current-meter and acoustic Doppler current profiler measurements in the Yucatan Channel. Those authors noted the difference between EOFs obtained from observations and their z-level models and EOFs calculated by Ezer et al. [2003] from the results of a terrain-following model. Here a new analysis is reported that explains this difference, and that also suggests the importance of shelf-edge meander mode of the core Loop Current in the channel. We show that the terrain-following model gives EOFs with characteristics similar to those observed when data from the upper slope and shelf in the western portion of the model channel are omitted. Modes 1 and 2 have tripole and dipole structures with energies (35%, 26%), respectively, of total energy, and correlate with ''slow'' vacillation of the core-current for periods >50 days. Exclusion of upper-slope and shelf data eliminates a short-period and energetic component inherent in Ezer et al.'s original mode 1 EOF. This mode correlates with frontal meanders of the core current over the shelf edge in the western portion of the channel. The short-period mode may be missing or underestimated in observational and z-level models' analyses, since there were only a few moorings over the upper slope and shelf, and z-level models have step-like topography with generally lower resolution in shallower seas.
Deep Sea Research and Oceanographic Abstracts, 1976
Measurements were made of the vertical distribution of microbial biomass in the water column and ... more Measurements were made of the vertical distribution of microbial biomass in the water column and sediments for two mid-Atlantic stations. Biomass estimates were based on measurements of total adenosine triphosphate (ATP) concentration. Both profiles indicate a large viable microbial population in near-surface waters (> 50 tzg C 1-1), followed by a characteristic decrease with depth. A second maximum (> 20 ~tg C l -t) occurred in both locations between 700 and 1000 m and corresponded to the depth of the oxygen minimum. Below 2200 m, the biomass remained relatively constant with depth (0.125 v-g C 1-1). Both profiles exhibited a six-fold increase in biomass I0 m above the sediment-water interface (4165, 6339 m), with an additional increase in the uppermost sediment layer (2.24 to 2.58 ~g C g-X). The biomass rapidly decreased in the sediments to less than 0.5 izg C g-X at a depth of 4 to 5 cm. Dissolved organic carbon (DOC) values ranged from 0.2 to 0.6 mg C 1-1 for the water samples. At the sediment-water interface values increased two-fold. Pore water DOC values ranged from 0.8 to 2"3 mg C 1 -t, decreasing with core depth.
The deep waters of the Caribbean Sea are renewed by sporadic flow over the two deep sills connect... more The deep waters of the Caribbean Sea are renewed by sporadic flow over the two deep sills connecting with the open Atlantic. In turn, the deep waters of the Gulf of Mexico are renewed by flow from the northwest Caribbean over the sill in Yucatan Channel, between Mexico and Cuba. So we examine the obvious question: if all this renewal water is coming in, what is going out? The view that emerges is a three-layer mean deep flow in the Caribbean and the Gulf. There is strong vertical shear in the water above 800 m associated with the primary upper-layer flow. Surprisingly, this shear continues to at least 400 m. In the three-layer scenario described here, the uppermost "deep layer" flows into the Gulf at depths of ~800-00 m as an extension of the upper-layer circulation. The deepest inflow is sporadic, just above sill depth. The third layer, containing the required mean return flow to achieve mass balance, is found between these two mean flows at depths of ~00 to ~900 m. There is little information about the horizontal pattern of this deep return flow. The transport in these deep flows into the Gulf and in the return flow is slightly less than Sv. These conclusions are inferred from the computed mean vertical shear, conservation of potential vorticity in the deep layers, the observed salinity gradients, and the assumption that there can be no net flow between 800 and 2000 m. The deep return flow of water from the Gulf of Mexico, having salinity ~34.96 psu, appears to flow from Yucatan Channel all the way back to Windward and Jungfern Passages, leaving the Caribbean above the entering deep renewal water.. InTroDuCTIon AnD BACkGrounD The essential ideas of renewal of deep water in the Caribbean Sea and Gulf of Mexico have been known for decades. The waters of the Atlantic spill over into the Caribbean through two passages that are ~2000 m deep. Plate a shows the positions of the major deep basins and the sills that connect them. The deep opening farthest east is the Anegada-Jungfern Passage Sill. From the work of Worthington in the '60s to the newer studies of Joyce et al. [999, 200] and MacCready et al. [999], it has usually been assumed that there is renewal over Windward Passage as well. recently Johns et al. [2004, personal communication] have made measurements in Windward Passage. There are, of course, many more observations in the near-surface layers than in the deeper waters flowing in over the sills. See, e.g., Johns et al. [2002], Wilson and Johns [997], Richardson [2004] and Mooers and Maul [998]. The openings at the far eastern end are only ~000 m deep. The density surface of Plate a, chosen to match one shown by Lozier et al. [995], lies near the middle of Title Book Series Copyright 200# XXXXXXXXXXX.
Variability in sea level at the longest periods observable in modern records has recently been fo... more Variability in sea level at the longest periods observable in modern records has recently been found to be well correlated with local atmospheric pressure. At shorter periods, however, longshore winds are known to be one of the primary mechanisms for forcing sea level variability on the eastern margins of the ocean. There is a remarkable ∼80 mm drop in mean sea level on both the eastern North Pacific and North Atlantic coasts between the late 1800s and early 1900s; it is found here to be in agreement with longshore wind forcing from the equator up to the latitude of the observed tide stations. Better-resolved data beginning in 1960 show that the delay near the annual period between wind forcing and sea level is approximately 1 month. The relative high in sea level in the late 1800s on the west coast of Europe appears to have propagated westward across the Atlantic as a long Rossby wave and then to have been seen on the east coast of the United States. Because many features in long-term sea level variability are correlated with wind forcing on time scales from annual to decades, it will be prudent to base conclusions about long-term sea level rise on the longest records available. The results here are based on forcing by longshore winds; the related issue of the extent to which open ocean wind curl may also be responsible is not addressed here, nor the extent to which coastal sea level observations are representative of the open ocean.
A Puzzling Disagreement between Observations and Numerical Models in the Central Gulf of Mexico
Journal of Physical Oceanography, 2013
Two large, independent sets of direct observations in the central Gulf of Mexico show a mean near... more Two large, independent sets of direct observations in the central Gulf of Mexico show a mean near-surface flow of ~10 cm s−1 to the west, concentrated in the northern and southern Gulf. Numerical models that the authors have examined do not produce this mean westward flow. The observed speeds appear to be almost an order of magnitude larger than the estimated errors; this paper studies the observations to estimate carefully the possible errors involved and compares the observations with model results. The flow to the west in the southern Gulf is presumably wind driven on the shallow parts of the shelf, and, in slightly deeper water at the outer edges of the shelf, is possibly the result of southward Sverdrup interior flow driven by the negative curl of the wind stress. In another possibly related issue, long-term deep current-meter observations in the northern Gulf at ~1000 m and below find flow to the west, whereas some models find flow to the east. The flow proposed here assumes a...
The long-term mean slope of sea level along the Pacific coast of the United States is estimated f... more The long-term mean slope of sea level along the Pacific coast of the United States is estimated for comparison with the rise from south to north reported by precise leveling. Oceanographic evidence does not support the leveling results. Steric levels at the coast relative to 1000 db strongly suggest that the slope reported by leveling is nonexistent. Careful examination of the 1000-db surface shows it to be a sufficiently level reference surface along the coast. Mean sea level at Neah Bay, Washington, is found to stand 9 cm lower than at San Diego, California, rather than 46 cm higher as suggested by leveling. A leveling error that could cause a slope of the observed sign and amount is discussed. The 9-cm difference found in the present study is consistent with the effect of changing latitude as the California Current flows south.
TSUCHIYA, M. 1968. Upper waters of the intertropical Pacific Ocean. The Johns Hopkins Oceanographic Studies, No. 4. The Johns Hopkins Press, Baltimore, Md. 50 p.+ 4 separate Figs. $8.50
Candela et al. [2003] have reported empirical orthogonal function (EOF) analyses based on 23-mont... more Candela et al. [2003] have reported empirical orthogonal function (EOF) analyses based on 23-month current-meter and acoustic Doppler current profiler measurements in the Yucatan Channel. Those authors noted the difference between EOFs obtained from observations and their z-level models and EOFs calculated by Ezer et al. [2003] from the results of a terrain-following model. Here a new analysis is reported that explains this difference, and that also suggests the importance of shelf-edge meander mode of the core Loop Current in the channel. We show that the terrain-following model gives EOFs with characteristics similar to those observed when data from the upper slope and shelf in the western portion of the model channel are omitted. Modes 1 and 2 have tripole and dipole structures with energies (35%, 26%), respectively, of total energy, and correlate with ''slow'' vacillation of the core-current for periods >50 days. Exclusion of upper-slope and shelf data eliminates a short-period and energetic component inherent in Ezer et al.'s original mode 1 EOF. This mode correlates with frontal meanders of the core current over the shelf edge in the western portion of the channel. The short-period mode may be missing or underestimated in observational and z-level models' analyses, since there were only a few moorings over the upper slope and shelf, and z-level models have step-like topography with generally lower resolution in shallower seas.
Deep Sea Research and Oceanographic Abstracts, 1976
Measurements were made of the vertical distribution of microbial biomass in the water column and ... more Measurements were made of the vertical distribution of microbial biomass in the water column and sediments for two mid-Atlantic stations. Biomass estimates were based on measurements of total adenosine triphosphate (ATP) concentration. Both profiles indicate a large viable microbial population in near-surface waters (> 50 tzg C 1-1), followed by a characteristic decrease with depth. A second maximum (> 20 ~tg C l -t) occurred in both locations between 700 and 1000 m and corresponded to the depth of the oxygen minimum. Below 2200 m, the biomass remained relatively constant with depth (0.125 v-g C 1-1). Both profiles exhibited a six-fold increase in biomass I0 m above the sediment-water interface (4165, 6339 m), with an additional increase in the uppermost sediment layer (2.24 to 2.58 ~g C g-X). The biomass rapidly decreased in the sediments to less than 0.5 izg C g-X at a depth of 4 to 5 cm. Dissolved organic carbon (DOC) values ranged from 0.2 to 0.6 mg C 1-1 for the water samples. At the sediment-water interface values increased two-fold. Pore water DOC values ranged from 0.8 to 2"3 mg C 1 -t, decreasing with core depth.
The deep waters of the Caribbean Sea are renewed by sporadic flow over the two deep sills connect... more The deep waters of the Caribbean Sea are renewed by sporadic flow over the two deep sills connecting with the open Atlantic. In turn, the deep waters of the Gulf of Mexico are renewed by flow from the northwest Caribbean over the sill in Yucatan Channel, between Mexico and Cuba. So we examine the obvious question: if all this renewal water is coming in, what is going out? The view that emerges is a three-layer mean deep flow in the Caribbean and the Gulf. There is strong vertical shear in the water above 800 m associated with the primary upper-layer flow. Surprisingly, this shear continues to at least 400 m. In the three-layer scenario described here, the uppermost "deep layer" flows into the Gulf at depths of ~800-00 m as an extension of the upper-layer circulation. The deepest inflow is sporadic, just above sill depth. The third layer, containing the required mean return flow to achieve mass balance, is found between these two mean flows at depths of ~00 to ~900 m. There is little information about the horizontal pattern of this deep return flow. The transport in these deep flows into the Gulf and in the return flow is slightly less than Sv. These conclusions are inferred from the computed mean vertical shear, conservation of potential vorticity in the deep layers, the observed salinity gradients, and the assumption that there can be no net flow between 800 and 2000 m. The deep return flow of water from the Gulf of Mexico, having salinity ~34.96 psu, appears to flow from Yucatan Channel all the way back to Windward and Jungfern Passages, leaving the Caribbean above the entering deep renewal water.. InTroDuCTIon AnD BACkGrounD The essential ideas of renewal of deep water in the Caribbean Sea and Gulf of Mexico have been known for decades. The waters of the Atlantic spill over into the Caribbean through two passages that are ~2000 m deep. Plate a shows the positions of the major deep basins and the sills that connect them. The deep opening farthest east is the Anegada-Jungfern Passage Sill. From the work of Worthington in the '60s to the newer studies of Joyce et al. [999, 200] and MacCready et al. [999], it has usually been assumed that there is renewal over Windward Passage as well. recently Johns et al. [2004, personal communication] have made measurements in Windward Passage. There are, of course, many more observations in the near-surface layers than in the deeper waters flowing in over the sills. See, e.g., Johns et al. [2002], Wilson and Johns [997], Richardson [2004] and Mooers and Maul [998]. The openings at the far eastern end are only ~000 m deep. The density surface of Plate a, chosen to match one shown by Lozier et al. [995], lies near the middle of Title Book Series Copyright 200# XXXXXXXXXXX.
Variability in sea level at the longest periods observable in modern records has recently been fo... more Variability in sea level at the longest periods observable in modern records has recently been found to be well correlated with local atmospheric pressure. At shorter periods, however, longshore winds are known to be one of the primary mechanisms for forcing sea level variability on the eastern margins of the ocean. There is a remarkable ∼80 mm drop in mean sea level on both the eastern North Pacific and North Atlantic coasts between the late 1800s and early 1900s; it is found here to be in agreement with longshore wind forcing from the equator up to the latitude of the observed tide stations. Better-resolved data beginning in 1960 show that the delay near the annual period between wind forcing and sea level is approximately 1 month. The relative high in sea level in the late 1800s on the west coast of Europe appears to have propagated westward across the Atlantic as a long Rossby wave and then to have been seen on the east coast of the United States. Because many features in long-term sea level variability are correlated with wind forcing on time scales from annual to decades, it will be prudent to base conclusions about long-term sea level rise on the longest records available. The results here are based on forcing by longshore winds; the related issue of the extent to which open ocean wind curl may also be responsible is not addressed here, nor the extent to which coastal sea level observations are representative of the open ocean.
A Puzzling Disagreement between Observations and Numerical Models in the Central Gulf of Mexico
Journal of Physical Oceanography, 2013
Two large, independent sets of direct observations in the central Gulf of Mexico show a mean near... more Two large, independent sets of direct observations in the central Gulf of Mexico show a mean near-surface flow of ~10 cm s−1 to the west, concentrated in the northern and southern Gulf. Numerical models that the authors have examined do not produce this mean westward flow. The observed speeds appear to be almost an order of magnitude larger than the estimated errors; this paper studies the observations to estimate carefully the possible errors involved and compares the observations with model results. The flow to the west in the southern Gulf is presumably wind driven on the shallow parts of the shelf, and, in slightly deeper water at the outer edges of the shelf, is possibly the result of southward Sverdrup interior flow driven by the negative curl of the wind stress. In another possibly related issue, long-term deep current-meter observations in the northern Gulf at ~1000 m and below find flow to the west, whereas some models find flow to the east. The flow proposed here assumes a...
The long-term mean slope of sea level along the Pacific coast of the United States is estimated f... more The long-term mean slope of sea level along the Pacific coast of the United States is estimated for comparison with the rise from south to north reported by precise leveling. Oceanographic evidence does not support the leveling results. Steric levels at the coast relative to 1000 db strongly suggest that the slope reported by leveling is nonexistent. Careful examination of the 1000-db surface shows it to be a sufficiently level reference surface along the coast. Mean sea level at Neah Bay, Washington, is found to stand 9 cm lower than at San Diego, California, rather than 46 cm higher as suggested by leveling. A leveling error that could cause a slope of the observed sign and amount is discussed. The 9-cm difference found in the present study is consistent with the effect of changing latitude as the California Current flows south.
TSUCHIYA, M. 1968. Upper waters of the intertropical Pacific Ocean. The Johns Hopkins Oceanographic Studies, No. 4. The Johns Hopkins Press, Baltimore, Md. 50 p.+ 4 separate Figs. $8.50
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Papers by W. Sturges