The vigor of Atlantic meridional overturning circulation (MOC) is thought to be vulnerable to global warming, but its short-term temporal variability is unknown so changes inferred from sparse observations on the decadal time scale of recent climate change are uncertain. We combine continuous measurements of the MOC (beginning in 2004) using the purposefully designed transatlantic Rapid Climate Change array of moored instruments deployed along 26.5°N, with time series of Gulf Stream transport and surface-layer Ekman transport to quantify its intra-annual variability. The year-long average overturning is 18.7 ± 5.6 sverdrups (Sv) (range: 4.0 to 34.9 Sv, where 1 Sv = a flow of ocean water of 106 cubic meters per second). Interannual changes in the overturning can be monitored with a resolution of 1.5 Sv.

http://science.sciencemag.org/content/sci/317/5840/935.full.pdf

Temporal Variability of the Atlantic Meridional Overturning Circulation at 26.5°N

Surface current patterns were used to map dispersal routes of pelagic larvae from 18 coral reef sites in the Caribbean. The sites varied, both as sources and recipients of larvae, by an order of magnitude. It is likely that sites supplied copiously from “upstream” reef areas will be more resilient to recruitment overfishing, less susceptible to species loss, and less reliant on local management than places with little upstream reef. The mapping of connectivity patterns will enable the identification of beneficial management partnerships among nations and the design of networks of interdependent reserves.

https://science.sciencemag.org/content/sci/278/5342/1454.full.pdf

Connectivity and Management of Caribbean Coral Reefs

Technical report series

Published values for the long-term, global mean sea level rise determined from tide gauge records exhibit considerable scatter, from about 1 mm to 3 mm/yr. This disparity is not attributable to instrument error; long-term trends computed at adjacent sites often agree to within a few tenths of a millimeter per year. Instead, the differing estimates of global sea level rise appear to be in large part due to authors' using data from gauges located at convergent tectonic plate boundaries, where changes of land elevation give fictitious sea level trends. In addition, virtually all gauges undergo subsidence or uplift due to postglacial rebound (PGR) from the last deglaciation at a rate comparable to or greater than the secular rise of sea level. Modeling PGR by the ICE-3G model of Tushingham and Peltier (1991) and avoiding tide gauge records in areas of converging tectonic plates produces a highly consistent set of long sea level records. The value for mean sea level rise obtained from a global set of 21 such stations in nine oceanic regions with an average record length of 76 years during the period 1880–1980 is 1.8 mm/yr±0.1. This result provides confidence that carefully selected long tide gauge records measure the same underlying trend of sea level and that many old tide gauge records are of very high quality.

Global sea level rise

Supporting Online Material for Temporal Variability of the Atlantic Meridional Overturning Circulation at 26.5°N

The most energetic events in the circulation of the Gulf of Mexico are the separation of large anticyclonic rings from the Loop Current. Building on previous work, the authors examine all the apparent rings since July 1973. This new dataset includes the satellite altimetry since 1992, providing a set of 34 consecutive ring formations. The primary advantage of altimetry is that the data remain available in the summer. One finding is that the ambiguity of whether or not a ring has separated is reduced, but not eliminated; the uncertainty with which separation “events” can be specified remains approximately 4 weeks, even with nearly continuous data. Primary peaks in the distribution of separation intervals are found at 6 and 11 months with a smaller peak at 9 months. If the spectrum is smoothed heavily enough, a peak in the distribution can be formed nearer 12 months, but this near-annual peak is a result more of the smoothing than of the data.

Frequency of Ring Separations from the Loop Current in the Gulf of Mexico: A Revised Estimate

The variation of sea level along continental boundaries is studied from a variety of data. Along the western boundaries of the Atlantic and Pacific oceans, sea level falls approximately 80 cm between the equator and 40°N or S. Along the eastern boundaries the change in level is about one-third this amount. This meridional slope is shown to be the correct amount required by the change with latitude of surface slope across the boundary currents. The meridional slope along the inshore edge of the Gulf Stream has the correct sign and magnitude to be balanced by the gradient of the Reynolds stresses. In the east-west direction, sea level along the Pacific coast of the United States stands about 70 cm higher than that along the Atlantic coast; two-thirds of this difference is concluded to be caused by density differences between the two oceans. The remaining third results because the east coast of the United States is inside the strong slope across a western boundary current, whereas the west coast is next to an eastern boundary current.

Sea level slope along continental boundaries

In this book, we describe our current state of knowledge on circulation in the Gulf of Mexico through 22 papers at the forefront of research. The view is selective rather than all-inclusive, with primary focus on circulation at the sea surface and at depth, including nearshore flow. In choosing topics, we have attempted to avoid the distinction between observations and models, as both are essential to advance our understanding of this exceptional body of water. We have also written for specialists and non-specialists alike in both science and industry: for those who work directly on the science associated with the Gulf, and for those whose work depends on the Gulf. And we refer here to physical oceanography, marine geology, sedimentology, coastal and estuarine science, as well as to the petrochemical and fishing industries.

Circulation in the Gulf of Mexico: Observations and Models: Sturges/Circulation in the Gulf of Mexico: Observations and Models

The Bermuda tide gauge record extends back to the early 1930s. That sea level fluctuations there are highly coherent with dynamic height from hydrographic data has two interesting implications. First, it should contain information about the low-frequency circulation of the Atlantic. Furthermore, because dynamic height contains information on heat storage, it might, on the limited timescales accessible in the record, also contain clues about climate. A simple model of wind forcing of the Atlantic from the African coast to Bermuda uses the Levitus mean density data to estimate the long Rossby wave speed as a function of longitude. Sea level and thermocline variability estimated this way are in remarkably good agreement with observations at periods of more than a few years duration. The peak-to-peak sea level signal is ∼18 cm, which is nearly 25% of the slope across the Gulf Stream at this latitude. The model results suggest that the variability is largest somewhat to the east of Bermuda; fluctuatio...

Wind Forcing of the Atlantic Thermocline along 32°N at Low Frequencies

Narragansett Bay is a weakly stratified estuary comprised of three connecting passages of varying depths. The vertical distribution of horizontal velocity was observed in the West Passage using moored current meters. The instantaneous motion was characterized by semi-diurnal tidal currents of amplitude 25–60 cm s−1. These currents exhibited a phase advance with depth (total water depth=12.8 m) ranging with lunar phase from 0–3 h. The net current time series obtained by filtering out motions at tidal and higher frequencies were found to be an order of magnitude less than the instantaneous motion and well correlated to the prevailing 2–10 m s−1 winds. For periodicities of 2–3 days, the coherence between the longitudinal components of wind and net near surface current was as high as 0.8 with the current lagging the wind by about 3 h. The mean near surface speed, obtained by averaging over one month, was 1.2±1.6 cm s−1. The large error bounds were a result of the large variability of the net current ...

Wilton Sturges

Papers

Frequency of Ring Separations from the Loop Current in the Gulf of Mexico: A Revised Estimate

Sea level slope along continental boundaries

Circulation in the Gulf of Mexico: Observations and Models: Sturges/Circulation in the Gulf of Mexico: Observations and Models

Wind Forcing of the Atlantic Thermocline along 32°N at Low Frequencies

Velocity Observations in the West Passage of Narragansett Bay: A Partially Mixed Estuary