Tuesday, 16 October 2012

Study area

NE Atlantic Semount depths

Important information for working out which oceanogrphic factors might influence larval transport. Depths are measures in metres below sealevel:

FeatureSummit (m)  Base (m)
Anton Dohrn Seamount521   2100
Bill Bailey Bank90  1000
Faeroe Bank70  1000 a couple of 1500 basins
George Bligh Bank80  1000 RH Basin 1500 RT
Hatton Bank500  1000 RH Basin 2500 N side
Hebrides Terrace Seamount100  1500 E side, 2200 W side
Lousy Bank70  1350
Rockall Bank0  1000 ledge, 2500 RT deepest, 1000 RH Basin
Rosemary Bank321  1550 + moat

Oceanography glossary

Baroclinic - a stratified fluid where the gradients of pressure and density are misalligned. Instability of broclinicity results in vorticity (eddies).

Barotropic -a stratified fluid where the gradients of pressure and density are alligned ( isobaric surfaces are also isopycnal and isothermal, baroclinic vector is zero and motions of fluid are strongly constrained)

Geostrophy -currents flowing parallel to isobars as a result of the coriolis force balancing the pressure gradient force. A geostrophic flow may be barotropic or baroclinic.

Halocline - the boundary (area of steepest gradient) separating two watermasses of different salinity in a stratified fluid

Internal waves - gravity waves occuring along pycnoclines. Can vary vastly in amplitude and frquency. Can be heightened by the lower water mass interfacing with rough topography.

Kelvin-Helmholtz instability - breaking internal waves, these occur when the Richardson number (the ratio of potential to kinetic energy) of a pycnocline drops below 0.25 (i.e. where the kinetic energy is high enough to break surface tension)

Pycnocline - the boundary (area of steepest gradient) separating two water masses of different density in a stratified fluid (may also be a halocline and/or thermocline)

Permanent Pycnocline - the boundary (area of steepest stable density gradient) which separates the upper waters where surface mixing occurs, and lower waters. This can restrict transport of nutrients between upper and lower layers and can inhibit the vertical migration of plankton. This can be diffused by shear produced turbulence, creating areas of upwelling.

Thermocline - the boundary (area of steepest gradient) separating two water masses of different temperatures in a stratified fluid

Tuesday, 9 October 2012

Seamounts - Online Resources

Might be worth noting, in case a source of data or a suppository for data post PhD


Adata portal for species record locations on seamounts workd wide. In UK/Irish waters they have data for:
Anton Dohrn
Rosemary bank
Hatton Bank
George Bligh Bank
Lousy Bank
Bill Bailey's Bank
All species record seem to be Lophelia pertusa or fish. Some unknow scleractinians. Most records taken from the literature, and many from the 18th centuary. Needs updating!


A flash map of the worlds seas with physical data including multibeam compiled for 1800 seamounts.
Records in this region:
Anton Dohrn - no multibeam
Hebrides Terrace - no multibeam
George Bligh Bank -1 multibeam file 2002
Bill Bailey's Bank - 2 multibeam files 1990, 2002
Lousy Bank - 2 multibeam files 1990, 2002
Faeroe Bank - 3 multibeam files 1990, 2002, 2002
Rosemary bank - 32 multibeam files 2003 (1x 2002)
(All in .mb format)

Monday, 8 October 2012

Connectivity definitions

This is skimmed straight from the WHOI benthic ecology and nearshore oceanography lab website and is rather helpful for straightening out definitions of phrases, thanks to them:

Larval transport
"Larval transport is defined as the horizontal translocation of a larva between points x1,y1 and x2,y2, where x and y are
horizontal axes, say, perpendicular and parallel to the coastline. In larval transport, only the spatial dimensions matter.
Although this definition ignores the vertical axis (z) for simplicity, this dimension is critical for larval transport"

Larval dispersal
"Larval dispersal refers to the spread of larvae from a spawning source to a settlement site. This definition is consistent with the terrestrial literature (natal dispersal in Clobert et al., 2001; Begon et al., 2006) that describes seed dispersal as the probability density function of the number of seeds versus distance from the adult source (i.e., the dispersal kernel) (Nathan and Muller-Landau, 2000; see Gerrodette, 1981, for a rare marine example)."
(See Scheltema, 1986 and Pineda, Hare and Sponaugle, 2007)

Population connectivity
"Population connectivity has been defined as the exchange of individuals among geographically separated subpopulations...By this definition, if the exchange is measured at the time of settlement, connectivity is essentially larval dispersal from one population to another"
(See Cowen et al., 2007, Oceanography, and Pineda, Hare and Sponaugle, 2007)

Reproductive population connectivity
The dispersal of individuals among subpopulations that survive to reproduce (see Pineda, Hare and Sponaugle, 2007)