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Sea temperatures from HMS Beagle

beaglesst

 

  • The graph shows a comparison between modern sea surface temperatures (SST) and temperatures measured during the 1831-1836 voyage of Captain Fitzroy and Charles Darwin on HMS Beagle.
  • Data collected by the Beagle were assigned to weekly buckets of a 53-week year.  Modern (1981-2017) weekly means at the ship locations were subtracted to give temperature “anomalies” experienced during the voyage.
  • The graph indicates that the Eastern Pacific ocean was anomalously cold during Darwin’s time at the Galapagos (shaded area). This looks consistent with a La Nina event.
  • Average temperatures during the voyage were 0.7°C cooler compared to an equivalent trip made today. The Beagle data are slightly more volatile compared to the modern SST dataset. This is to be expected because the latter is an average over time and space (1° x 1°) whereas the Beagle measurements were local in time and space.
  • Measurements at anchor and at interpolated coordinates are omitted.
  • HMS Beagle data derived from the ICOADS database, which is a very rich source of shipping data with all kinds of application.

 

Antipodean Islands

DCIM100GOPROGOPR0701.JPG

Campbell Island

On a recent trip, I visited Campbell Island, the Southern-most of New Zealand’s extraordinary sub-antarctic islands. A fellow visitor from Ireland pointed out that Campbell is the land mass furthest from home i.e. Campbell Island is the true Irish antipode.  I had always assumed (wrongly) that this distinction was held by the eponymous Antipodes Island.

The situation is shown below. Black dots mark the centroids of the small sub-antarctic islands after reflection through the centre of the earth.

antipodes

Colours show which dot is nearest, using geodesic distances on an ellipsoidal earth. This is just an ordinary Voronoi diagram, expect that the curvature of the Earth is taken into account accurately. (distGeo() function from R‘s geosphere package).

Campbell is the antipode for Ireland and Scotland, while Antipodes Island is antipode for England, Wales and Normandy (except for Anglesea and a sliver of Cumbria).