Time filter

Source Type

Meinen C.S.,Atlantic Oceanographic and Meteorological Laboratory | Luther D.S.,University of Hawaii at Manoa
Deep-Sea Research Part I: Oceanographic Research Papers | Year: 2016

Savidge (2016) raises a concern about how the spatial averaging embodied in our Gulf Stream analysis of vertical coherence (Meinen and Luther, 2016) might contribute to the low coherence found. This response addresses the concerns raised in the Savidge (2016) short comment. © 2016. Source

Everroad R.C.,University of Oregon | Everroad R.C.,RIKEN | Wood A.M.,University of Oregon | Wood A.M.,Atlantic Oceanographic and Meteorological Laboratory
Molecular Phylogenetics and Evolution | Year: 2012

In marine Synechococcus there is evidence for the adaptive evolution of spectrally distinct forms of the major light harvesting pigment phycoerythrin (PE). Recent research has suggested that these spectral forms of PE have a different evolutionary history than the core genome. However, a lack of explicit statistical testing of alternative hypotheses or for selection on these genes has made it difficult to evaluate the evolutionary relationships between spectral forms of PE or the role horizontal gene transfer (HGT) may have had in the adaptive phenotypic evolution of the pigment system in marine Synechococcus. In this work, PE phylogenies of picocyanobacteria with known spectral phenotypes, including newly co-isolated strains of marine Synechococcus from the Gulf of Mexico, were constructed to explore the diversification of spectral phenotype and PE evolution in this group more completely. For the first time, statistical evaluation of competing evolutionary hypotheses and tests for positive selection on the PE locus in picocyanobacteria were performed. Genes for PEs associated with specific PE spectral phenotypes formed strongly supported monophyletic clades within the PE tree with positive directional selection driving evolution towards higher phycourobilin (PUB) content. The presence of the PUB-lacking phenotype in PE-containing marine picocyanobacteria from cyanobacterial lineages identified as Cyanobium is best explained by HGT into this group from marine Synechococcus. Taken together, these data provide strong examples of adaptive evolution of a single phenotypic trait in bacteria via mutation, positive directional selection and horizontal gene transfer. © 2012 Elsevier Inc.. Source

Enfield D.B.,Atlantic Oceanographic and Meteorological Laboratory | Enfield D.B.,Cooperative Institute for Marine and Atmospheric Studies | Cid-Serrano L.,University of Concepcion | Cid-Serrano L.,Andres Bello University
International Journal of Climatology | Year: 2010

Analysis of recent literature finds weaknesses in arguments to the effect that the Atlantic multidecadal oscillation (AMO) - roughly 50-90 year fluctuations in North Atlantic sea surface temperatures - is externally forced by anthropogenic aerosols and greenhouse gases rather than an internal climate mode, plus indications from other sources that the contrary may be true. We are led to the conclusion that the AMO is probably comprised of both natural and anthropogenic forcing in ways that preclude a physically based separation of the two, using the limited historical data sets. A straightforward quadratic fitting of trend to temperature data accounts for some of the 20th century nonlinearity in secular warming and separates the secular and multidecadal components of variability without inherent assumptions about the nature of the multidecadal fluctuations. Doing this shows that the 20th century secular ocean warming in the North Atlantic is about equal to the peak-to-peak amplitude of the multidecadal fluctuations. However, over the last quarter-century (1975-2000) the most recent multidecadal warming has been almost three times the secular sea surface temperature (SST) increase over the main development region (MDR) for major Atlantic hurricanes. In the last quarter-century the multidecadal increase in late summer Atlantic warm pool (AWP) size (area of SSTs in excess of 28°C) has been 36%, and the secular increase, 14%. Projections to the year 2025 show that the cumulative change in summer warm pool size since 1975 will depend critically on whether a subsequent cooling in the multidecadal cycle occurs, comparable to the warming between 1975 and 2000 AD. This places a high premium on understanding to what extent the AMO is a man-made or a natural phenomenon. © 2009 Royal Meteorological Society. Source

Holthuijsen L.H.,Technical University of Delft | Powell M.D.,Atlantic Oceanographic and Meteorological Laboratory | Pietrzak J.D.,Technical University of Delft
Journal of Geophysical Research: Oceans | Year: 2012

Waves breaking at the ocean surface are important to the dynamical, chemical and biological processes at the air-sea interface. The traditional view is that the white capping and aero-dynamical surface roughness increase with wind speed up to a limiting value. This view is fundamental to hurricane forecasting and climate research but it has never been verified at extreme winds. Here we show with observations that at high wind speeds white caps remain constant and at still higher wind speeds are joined, and increasingly dominated, by streaks of foam and spray. At surface wind speeds of ∼40 m/s the streaks merge into a white out, the roughness begins to decrease and a high-velocity surface jet begins to develop. The roughness reduces to virtually zero by ∼80 m/s wind speed, rendering the surface aero-dynamically extremely smooth in the most intense part of extreme (or major) hurricanes (wind speed > 50 m/s). A preliminary assessment shows that cross swell, dominant in large regions of hurricanes, allows the roughness under high wind conditions to increase considerably before it reduces to the same low values. © 2012. American Geophysical Union. All Rights Reserved. Source

Frajka-Williams E.,University of Southampton | Johns W.E.,University of Miami | Meinen C.S.,Atlantic Oceanographic and Meteorological Laboratory | Beal L.M.,University of Miami | Cunningham S.A.,Scottish Association for Marine Science
Geophysical Research Letters | Year: 2013

The Gulf Stream in the Atlantic carries warm water northwards and forms both the return closure of the subtropical gyre as well as the upper limb of the meridional overturning circulation. Recent time series recorded east of the Bahamas at 26°N indicate that from May 2009 to April 2011, in contrast with past observations, the northward flowing Antilles Current covaried with the Gulf Stream in the Florida Straits-the Florida Current-even though the Florida and Antilles Currents are separated by banks and islands spanning 150 km. The peak-to-trough amplitude of transport variations during this period was 15×106m3 s-1 for the Florida Current and 12×106m3 s-1 for the Antilles Current, at time scales of 50 days to a year. From satellite observations, we show that the fluctuations in both the Florida and Antilles Currents between May 2009 and April 2011 are driven by eddy activity east of the Bahamas. Since the Florida Current time series is a critical time series for the state of the oceans, and often compared to climate models, this newly identified source of variability needs careful consideration when attributing the variability of the Florida Current to changes in the larger-scale circulations (e.g., gyre and overturning) or wind forcing. © 2013. American Geophysical Union. All Rights Reserved. Source

Discover hidden collaborations