observations of the florida and yucatan currents from a

Observations of the Florida and Yucatan Currents from a Caribbean Cruise Ship

CLEMENT ROUSSET AND LISA M. BEAL

Division of Meteorology and Physical Oceanography, Rosenstiel School of Marine and Atmospheric Science,

University of Miami, Miami, Florida

(Manuscript received 16 February 2010, in final form 17 March 2010)

ABSTRACT

The Yucatan and Florida Currents represent the majority of the warm-water return path of the global ther-

mohaline circulation through the tropical/subtropical North Atlantic Ocean. Their transports are quantified and

compared by analyzing velocity data collected aboard the cruise ship Explorer of the Seas. From 157 crossings

between May 2001 and May 2006, the mean transport of the Florida Current at 268N was estimated to be 30.8 6

3.2 Sv (1 Sv [ 106 m3 s21), with seasonal amplitude of 2.9 Sv. Upstream, the Yucatan Current was estimated

from 90 crossings to be 30.3 6 5 Sv, with seasonal amplitude of 2.7 Sv. These two currents are shown to be

linked at seasonal time scales. Hence, contrary to former results, it was found that transports through the

Florida Straits and the Yucatan Channel are similar, with the implication that only small inflows occur through

minor channels between them.

1. Introduction

The Yucatan Channel and the Florida Straits carry the

upper limb of the meridional overturning circulation in

the tropical/subtropical North Atlantic Ocean and thus

have a significant impact on the global climate. The Florida

Current has been intensely studied, and submarine cable

measurements over more than 20 years show that its mean

transport at 278N is 32.3 6 3.2 Sv (1 Sv [ 106 m3 s21)

(Larsen 1992). This transport is fed from the south by

a main flow through the Yucatan Channel and by minor

flows through the Old Bahama and Northwest Provi-

dence Channels (Fig. 1).

The Yucatan Channel has been far less studied. Early

geostrophic transport estimates ranged from 23 to 33 Sv

(Schlitz 1973), but the classical geostrophic calculation

might not provide accurate estimates because there is no

definite level of no motion in the channel (Ochoa et al.

2001). Later on, by balancing the transport budget for

the Caribbean passages, a nominal transport of 28.5 Sv

was attributed to this channel (Johns et al. 2002). How-

ever, there was large uncertainty because of a lack of

observations in some passages. Two years of more recent

direct measurements across the channel (‘‘Canek’’ pro-

gram, August 1999–June 2001) gave a mean transport of

23.1 6 3.1 Sv (Candela et al. 2003). The authors noted

the large discrepancy between the Yucatan Channel and

Florida Strait transports and ventured the hypothesis

that it could be related to poorly known transports through

Old Bahama and Northwest (NW) Providence Channels.

However, sparse measurements estimated these flows at

only 1 or 2 Sv (Leaman et al. 1995; Atkinson et al. 1995),

implying that the discrepancy could be due to high in-

terannual variability in the various passages.

In this study, we compare the fluxes through the Florida

Strait at 268N and the Yucatan Channel using new mea-

surements. During 2001–06, the Royal Caribbean Cruise

Ship Explorer of the Seas, outfitted with two acoustic

Doppler current profilers (ADCP), collected ocean ve-

locity data throughout the intra-Americas seas. The two

ADCPs of frequencies 38 and 150 kHz penetrate to 1200

and 250 m, respectively. In this study, the 38-kHz ADCP

is used to analyze velocity structure, transport, and vari-

ability, whereas the 150 kHz is used for validating and

improving surface velocities. In addition to these mea-

surements, we use the Hybrid Coordinate Ocean Model

(HYCOM) in its global 1/128 data-assimilative configura-

tion (e.g., Chassignet et al. 2007) to estimate missing flows

where there are gaps in the data. A detailed description of

the ADCP data quality and final processing is given by

Beal et al. (2008).

Corresponding author address: C. Rousset, MPO, RSMAS,

University of Miami, 4600 Rickenbacker Causeway, Miami, FL

33149.

E-mail: [email protected]

JULY 2010 R O U S S E T A N D B E A L 1575

DOI: 10.1175/2010JPO4447.1

� 2010 American Meteorological SocietyUnauthenticated | Downloaded 06/04/22 12:29 PM UTC

2. Results

a. Time-mean transports

The Florida Current was better sampled than the

Yucatan Current, owing to the consistency and orien-

tation of the cruise tracks and the shallower depth of

the Florida Straits (Fig. 1). The calculation of flux es-

timates across the Florida Straits follows the technique

of Beal et al. (2008). In brief, 157 good crossings were

obtained over which tidal velocities using the Oregon

State University (OSU) tidal prediction model (Egbert

et al. 1994; Egbert and Erofeeva 2002) were estimated

and removed. The shallowest measurements were at

60 m, and analysis of the 150-kHz ADCP showed that

the most realistic surface extrapolation was to apply a

constant velocity above. A gap between the deepest cell

and the bottom equal to 13% of the total water depth

(caused by acoustic sidelobe interference) was filled

with a constant vertical shear extrapolation. The mean

transport was adjusted for heading-dependent gyro-

compass biases, applying two-thirds of the bias to the

eastbound tracks and one-third to the westbound tracks

(Beal et al. 2008). Figure 2 shows a summary of these

corrections. The mean Florida Current transport was

FIG. 1. Mean surface currents (0–212 m) from the Explorer of the Seas ADCP dataset superimposed on the bathymetry of the Caribbean

Sea. Sections A, B, C, and D cross the Yucatan Current, and the red arrows represent the Florida Current at 268N.

1576 J O U R N A L O F P H Y S I C A L O C E A N O G R A P H Y VOLUME 40

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then estimated to be 30.8 6 3.2 Sv, with a standard error

of 0.3 Sv.

For the Yucatan transport, four different cruise tracks

(A, B, C, and D) crossed the channel at varying incidence

angle, and our measurements do not penetrate to the sea

bed, making flux calculations more difficult (Fig. 1).

Transport was estimated as for the Florida Current, with

the following exceptions. First, the gap caused by the

acoustic sidelobe interference was filled by constant

vertical shear where large flows exist over the depth of

the Yucatan Current (700 m) and by a no-slip condition

below (700–1200 m). Second, we account for missing flow

at the coasts and at depths greater than 1200 m by cal-

culating the transports through each of the measured

sections in HYCOM and comparing them with their

equivalents across closed, full-depth sections. Third,

section D is treated somewhat differently because it

crosses the Yucatan Current upstream of the channel.

Our data and HYCOM show that the current here con-

tinues through the channel while an offshore anticyclonic

gyre recirculates to the south of it. Therefore, we account

for the varying width of the throughflow by adjusting the

distance along the track over which we integrate trans-

port, dependent on the position of the offshore flank of

the gyre. However, because the mean transport along the

rest of the entire section D (out to the Cayman Islands) is

close to zero, this adjustment does not change the mean

transport by more than 0.2 Sv relative to a fixed-length

calculation. The resultant transports lie between those

of the other sections. A summary of all of the extrapo-

lations and corrections is given in Fig. 2. By averaging the

90 crossings (11 in section A, 3 in section B, 23 in section C,

FIG. 2. An illustration of the five steps in our mean transport calculations for each of the four

sections A, B, C, and D across the Yucatan Current (colors as for Fig. 1), plus their average

(black line). The red line shows the same for the Florida Current. Starting with the processed

dataset (raw), the steps are 1) detiding, 2) extrapolation at the surface between 0 and

60 m (constant velocity layer), 3) deep extrapolation for sidelobe interference, 4) estimation of

missing flows at the coast and below 1200 m using the HYCOM 1/128 simulation, and 5) cor-

rection for the heading-dependent bias. Note that the transports of the Yucatan and Florida

Currents are within ;1 Sv both before and after extrapolations and corrections. Note also that

;80% of the total adjustment is performed by the surface extrapolation, which increases the

transport equally for the Florida and Yucatan Currents, whereas the rest of the adjustment

accumulates to less than 1 Sv. In particular for the Yucatan Current, the deep extrapolation for

sidelobe interference adds only 0.1 Sv to the mean transport, whereas the missing flow at the

coast and below 1200 m is 20.7 Sv, with one-half of this owing to the missing deep flows.

Moreover, note here that the heading-dependent gyrocompass bias in the Yucatan Current

is reflected in the comparison of the mean transport of 33 Sv from the 35 eastbound tracks and

28.9 Sv from the 55 westbound tracks (independent of the four different sections). And,

following the gyrocompass bias attribution established for the Florida Current (Beal et al. 2008;

using bottom-tracking data, which are not available here), the heading correction in the

Yucatan Current leads to a 20.2 Sv change in the global-mean transport (0.5 Sv if we assume

equal bias between the eastward and westward tracks).



and 53 in section D), we find a mean Yucatan Current

transport of 30.3 6 8.8 Sv, with a standard error of 1.1 Sv.

Applying the Student’s t test gives 99% confidence that

the mean transport lies between 28.2 and 33.6 Sv.

Our mean Florida Strait transport is consistent with

the cable measurements, which include inflow from the

NW Providence Channel (Baringer and Larsen 2001).

The difference between cable transport at 278N and ours

at 268N implies a NW Providence Channel transport of

1.5 Sv, which is close to previous estimates [1.2 Sv in

Leaman et al. (1995); 0.9 Sv in Hamilton et al. (2005)].

However, our Yucatan Current transport differs by

6 standard errors from Canek (Sheinbaum et al. 2002),

and we find no discrepancy between the Florida and

Yucatan Current mean transports. This finding—that the

Florida and Yucatan Currents are similar—is indepen-

dent of the extrapolations and corrections required for

our transport calculation, as shown in Fig. 2. Our results

imply a 0.5 Sv mean flow through the Old Bahama

Channel (although this is within our estimated uncer-

tainty), which is smaller than a previous estimate of 1.9 Sv

(Atkinson et al. 1995). Old Bahama and NW Providence

Channels would then account for about 2 Sv together,

which is not strongly different from the generally ac-

cepted 3 Sv (Johns et al. 2002; Hamilton et al. 2005).

The small transport difference between the Yucatan

Channel and Florida Straits found in this study is also

reflected in the HYCOM simulation and in the 1/158

numerical experiment conducted in this region with a

z-coordinate ocean model (Jouanno et al. 2008). In sum-

mary, our measurements suggest a new paradigm for the

transport budget of the northern passages of the intra-

Americas seas. The mean transports of the Florida and

Yucatan Currents differ by less than 1 Sv, and hence flows

in minor passages are small.

We note that, at 8.8 Sv, the standard deviation of our

Yucatan Current transport is much larger than the 3 or

4 Sv expected from previous observational and numerical

studies (Candela et al. 2003). We investigated several

possible reasons for this discrepancy based on the fol-

lowing sampling errors: 1) fluctuations of the deep flow

below 1200 m that we do not measure, 2) missing flow at

the coast, and 3) the differing lengths of the four sec-

tions sampled. In the first case, both the Canek results

(Sheinbaum et al. 2002) and HYCOM show that fluc-

tuations of the deep flow have negligible impact on the

fluctuations of the total water column (#0.2 Sv), although

of themselves they can be large (standard deviation

2.2 Sv). For the second point, the model shows that

closed sections have a 20% reduction of the standard de-

viation. For the third, both HYCOM and our data show

that transport variability increases the farther south

and longer the section is. We interpret this as the larger

impact of the recirculating flow from the anticyclonic

gyre in the more southerly sections, which increases the

standard deviation of the transport by 25% without af-

fecting the mean. Overall, we account for about one-half

of our standard deviation in sampling errors and hence

estimate the oceanic standard deviation to be 4.5–5 Sv.

b. Vertical and horizontal structure of the current

The mean structure of the Yucatan Current is best

represented by section D, because it is almost perpen-

dicular to the isobaths and thus to the current direction,

although it is south of the channel (Fig. 1). The northward

flow is 170–180 km wide, and the core of the current is

located above the western shelf slope, close to the coast,

with a peak speed of 130 cm s21 at the surface (Fig. 3a).

During the same period, the Florida Current showed a

peak of 170 cm s21 (Fig. 3c). The part of the Yucatan

Current that flows over bathymetry deeper than about

2500 m (5–6 Sv according to the measurements) typically

recirculates south of Cuba to return across section D as

the southward flow between 848 and 85.58W in the center

of the Yucatan Basin. Analysis of the model shows that

this flow forms an anticyclonic gyre, as depicted also by

recent surface drifter trajectories (Richardson 2005).

Sections A, B, and C (Fig. 1) also capture some of this

southerly flow (Emilsson 1971; Ochoa et al. 2001) at their

eastern ends. The variability of the Yucatan Current at

section D (Fig. 3b) is surface intensified, with a maximum

located at the front between the current and the anti-

cyclonic gyre, indicating that the position of the front is

highly variable.

Figure 3d shows the transport per unit depth for the

Florida and Yucatan Currents. The Yucatan Current has

a deeper extension than the Florida Current. A compari-

son of the two transport-per-unit-depth profiles shows that

the Yucatan transport is 1.6 Sv less than the Florida

transport integrated from the surface to 450 m, whereas

it is 1.1 Sv stronger below. The required upwelling of

waters into the surface 450 m of the Florida Current,

plus the intensification of the flow, is consistent with

a combination of the tilting and uplifting of isotherms

between the Yucatan and Florida Currents (see Fig. 2 in

Leaman et al. 1987 and Fig. 18 in Candela et al. 2003, not

shown), plus the contribution of the Old Bahama Channel.

c. Time series and seasonal cycles

The time series from the individual crossings of the

Florida and Yucatan Currents are shown in Fig. 4a (upper

panels), together with the cable transports at 278N. The

direct correlations between these three time series are

very low (0.2–0.3) as a result of several factors. First, the

dominant short-period variability [,20 days in the Florida

Current (Lee et al. 1985) and ,40 days in the Yucatan



Current (Abascal et al. 2003)] is aliased by low temporal

sampling. Second, the NW Providence and Old Bahama

Channel inflows lie between these sections and can have

substantial instantaneous fluxes. Third, there are high

sampling errors associated with individual Yucatan sec-

tions, as discussed above, which inflate the range of in-

stantaneous values to 12–49 Sv, as compared with 15–33 Sv

found during Canek (Sheinbaum et al. 2002).

By averaging our data over longer time scales, we ex-

pect better correlations. Figure 4a (bottom panel) shows

all three time series filtered using a 3-month Hanning

window. Correlations are larger (0.4–0.5), although dif-

ferences do persist, specifically from mid-2003 to early

2004 in the Yucatan Current. The correlations based on

weekly-mean datasets are the same as those described

here and based on daily interpolated datasets. With

90 crossings over 4 yr, the Yucatan Channel was occupied

a little less than twice per month, and we attempt to re-

solve its seasonal cycle and compare it with the Florida

Current. Transports were averaged month by month over

their respective periods of sampling in the two passages

(Fig. 4b). The two currents exhibit similar seasonal vari-

ability, with a maximum in summer preceded and followed

by a minimum in spring and autumn. The amplitudes of

their cycles are also similar, 2.9 Sv for Florida at 268N

and 2.7 Sv for Yucatan, despite the elevated sampling

error in the latter. Because of the relatively small number

of measurements in each month (respectively, 13 and

7.5 on average in the Florida and Yucatan Currents),

we note that the standard errors are the same order as

the annual cycle, and hence the statistical significance

of these results is marginal. However, our annual cycles

corroborate with numerical simulations (Johns et al. 2002;

Candela et al. 2003) and with the cable data [the Canek

program was not long enough to resolve the seasonal

cycle, as noted by Candela et al. (2003)], and this brings

subjective confidence to our results and suggests that these

three locations are strongly linked at seasonal time scales.

Thus, the wind forcing over the subtropical Atlantic Ocean,

the Caribbean Sea, and the Florida Straits, which is

thought to be responsible for seasonal fluctuations in

the Florida Current (Schott et al. 1988), also appears

FIG. 3. (a) The 4-yr-mean (2002–06) cross-sectional velocity at section D and (b) its standard deviation. (c) The

5-yr-mean (2001–06) cross-sectional velocity in the Florida Strait at 268N. Note that the x axis scaling is changed

between (a) and (c). (d) Mean transport per unit depth (Sv m21) of the Yucatan Current (combination of all four

sections; black line), and of the Florida Current at 268N (red line), together with their standard deviations (gray and

pink shading, respectively). The mean transports above and below the isodepth of 450 m are also indicated for both

passages.



to have a dominant role in the Yucatan Current. It is worth

noting here that the average of the monthly-mean trans-

ports differs by only 0.2 Sv from the direct means reported

above, and therefore seasonal sampling biases are small.

3. Conclusions

Five years of ocean velocity data have been collected

aboard a cruise ship and used to characterize the flows

of the Yucatan and Florida Currents. Contrary to results

from Canek, we find that the mean transports through the

two passages are similar, which is in agreement with es-

timated flows in minor passages and the overall mass

budget for the region. We have also observed, for the first

time, that the two currents are strongly linked at seasonal

time scales.

Owing to the opportunistic sampling, our measurements

were examined carefully for errors, biases, and gaps (see

section 2). Except for the surface extrapolation (which

increases the transport equally for the Florida and Yucatan

Currents), these adjustments accumulate to less than

1 Sv (Fig. 2), which is not enough to account for the dif-

ference between the Yucatan transport reported here and

the 23.1 6 3.1 Sv reported previously. The disagreement

between these two estimates is puzzling, and a fuller in-

vestigation is part of an ongoing study. Because our ob-

servations do not overlap in time, there is the possibility

of interannual variability playing a role. However, cable

measurements in the Florida Current indicate interan-

nual variability of less than 2 Sv between the two time

periods.

Acknowledgments. The Explorer of the Seas shipboard

ADCP program is a collaboration between Royal Carib-

bean International, RSMAS at the University of Miami,

and AOML. This work was supported by the National

Science Foundation Grant OCE 0728897. The Florida

Current cable data are made freely available by AOML

on the Internet (www.aoml.noaa.gov/phod/floridacurrent)

and are funded by the NOAA Office of Climate Obser-

vations. We thank the reviewers for their help to improve

this manuscript.

REFERENCES

Abascal, A. J., J. Sheinbaum, J. Candela, J. Ochoa, and A. Badan,

2003: Analysis of flow variability in the Yucatan Channel.

J. Geophys. Res., 108, 3381, doi:10.1029/2003JC001922.

Atkinson, L. P., T. Berger, P. Hamilton, E. Waddell, K. Leaman,

and T. N. Lee, 1995: Current meter observations in the Old

Bahama Channel. J. Geophys. Res., 100, 8555–8560.

Baringer, M. O., and J. C. Larsen, 2001: Sixteen years of Florida

Current transport at 278N. Geophys. Res. Lett., 28, 3179–3182.

Beal, L. M., J. M. Hummon, E. Williams, O. B. Brown, W. Baringer,

and E. J. Kearns, 2008: Five years of Florida Current structure

and transport from the Royal Caribbean cruise ship Explorer

of the Seas. J. Geophys. Res., 113, C06001, doi:10.1029/

2007JC004154.

Candela, J., S. Tanahara, M. Crepon, B. Barnier, and J. Sheinbaum,

2003: Yucatan Channel flow: Observations versus CLIPPER

FIG. 4. (a) The top panels show the time series of the transport

(Sv) through the Yucatan Channel (in black), the Florida Strait at

268N (in red), and the Florida Strait at 278N (cable measurements,

in gray) between 2001 and 2006. For visualization, a linear inter-

polation was used to fill the gaps in the time series. The mean

transports and their standard deviations are indicated. For the

Yucatan time series, the transports through each of the four sec-

tions are represented by markers with the same colors as in Fig. 1.

The bottom panel shows the filtered time series of the transports

(Sv) using a Hanning window of 3 months. Colors are the same as

for the top panels. (b) Mean seasonal cycles of the transports (Sv)

through the Yucatan Channel (2002–06), the Florida Strait at 268N

(2001–06), and the Florida Strait at 278N (2001–06). Transports

were averaged month by month over their respective periods of

sampling in the three passages, with the first month corresponding

to January and the 12th month corresponding to December. Colors

are the same as in (a).



ATL6 and MERCATOR PAM models. J. Geophys. Res., 108,

3385, doi:10.1029/2003JC001961.

Chassignet, E. P., and Coauthors, 2007: The HYCOM (HYbrid

Coordinate Ocean Model) data assimilative system. J. Mar.

Syst., 65, 60–83.

Egbert, G. D., and S. Y. Erofeeva, 2002: Efficient inverse modeling

of barotropic ocean tides. J. Atmos. Oceanic Technol., 19,

183–204.

——, A. F. Bennett, and M. G. G. Foreman, 1994: TOPEX/

Poseidon tides estimated using a global inverse model. J. Geo-

phys. Res., 99, 24 821–24 852.

Emilsson, I., 1971: Note on the counter current in the Yucatan

Channel and the western Cayman Sea. Geofis. Int., 11,

139–149.

Hamilton, P., J. C. Larsen, K. D. Leaman, T. N. Lee, and

E. Waddell, 2005: Transports through the Straits of Florida.

J. Phys. Oceanogr., 35, 308–322.

Johns, W. E., T. L. Townsend, D. M. Fratantoni, and W. D. Wilson,

2002: On the Atlantic inflow to the Caribbean Sea. Deep Sea

Res. I, 49, 211–243.

Jouanno, J., J. Sheinbaum, B. Barnier, J.-M. Molines, L. Debreu,

and F. Lemarie, 2008: The mesoscale variability in the Ca-

ribbean Sea. Part I: Simulations and characteristics with an

embedded model. Ocean Modell., 23, 82–101.

Larsen, J., 1992: Transport and heat flux of the Florida Current at

278N derived from cross-stream voltages and profiling data:

theory and observations. Philos. Trans. Roy. Soc. London,

A338, 169–236.

Leaman, K. D., R. L. Molinari, and P. S. Vertes, 1987: Structure

and variability of the Florida Current at 278N: April 1982–July

1984. J. Phys. Oceanogr., 17, 565–583.

——, P. S. Vertes, L. P. Atkinson, and T. N. Lee, 1995: Transport,

potential vorticity, and current/temperature structure across

Northwest Providence and Santaren Channels and the Florida

Current off Cay Sal Bank. J. Geophys. Res., 100, 8561–8569.

Lee, T. N., F. A. Schott, and R. Zantopp, 1985: Florida Current:

Low-frequency variability as observed with moored current

meters during April 1982 to June 1983. Science, 227, 298–302.

Ochoa, J., J. Sheinbaum, A. Badan, J. Candela, and D. Wilson,

2001: Geostrophy via potential vorticity inversion in the

Yucatan Channel. J. Mar. Res., 59, 725–747.

Richardson, P. L., 2005: Caribbean Current and eddies as observed

by surface drifters. Deep Sea Res. II, 52, 429–463.

Schlitz, R. J., 1973: Net total transport and net transport by water

mass categories for Yucatan Channel, based on data for April

1970. Ph.D. dissertation, Texas A&M University, 107 pp.

Schott, F. A., T. N. Lee, and R. Zantopp, 1988: Variability of

structure and transport of the Florida Current in the period

range of days to seasonal. J. Phys. Oceanogr., 18, 1209–1230.

Sheinbaum, J., J. Candela, A. Badan, and J. Ochoa, 2002: Flow

structure and transport in the Yucatan Channel. Geophys. Res.

Lett., 29, 1040, doi:10.1029/2001GL013990.



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