Tuesday, March 31, 2009

Pliocene Warm Period

Greatly Expanded Tropical Warm Pool and Weakened Hadley Circulation in the Early Pliocene in Science.
The Pliocene warm interval has been difficult to explain. We reconstructed the latitudinal distribution of sea surface temperature around 4 million years ago, during the early Pliocene. Our reconstruction shows that the meridional temperature gradient between the equator and subtropics was greatly reduced, implying a vast poleward expansion of the ocean tropical warm pool. Corroborating evidence indicates that the Pacific temperature contrast between the equator and 32°N has evolved from 2°C 4 million years ago to 8°C today. The meridional warm pool expansion evidently had enormous impacts on the Pliocene climate, including a slowdown of the atmospheric Hadley circulation and El NiƱo–like conditions in the equatorial region. Ultimately, sustaining a climate state with weak tropical sea surface temperature gradients may require additional mechanisms of ocean heat uptake (such as enhanced ocean vertical mixing).

Orbital resonance and Solar cycles

Orbital resonance and Solar cycles
A detailed analysis of the couplings between the orbits of the planets and possible relationships with solar activity and the earth's climate. Nice graphics.

Is the Milky Way "Rotation Curve" Real?

Indications of an Unmodelled Component in Spectrographic Measurements of Local Stars
The Milky Way's rotation curve appears to be flat, based on the measured doppler shifts of interstellar gas. In contrast, the authors find that the rotation curve of the motions of local stars is not flat. Is the explanation an unmodelled component to the spectrographic measurements?

Monday, March 30, 2009

Solar System Dark Matter

Solar System Dark Matter by Stephen L. Adler:
I review constraints on solar system-bound dark matter, and discuss the possibility that dark matter could be gravitationally bound to the earth and other planets. I briefly survey various empirical constraints on such planet-bound dark matter, and discuss effects it could produce if present, including anomalous planetary heating and flyby velocity changes

Saturday, March 21, 2009

Whales and Dolphins, Oh My

In addition to Humpback Whales, we sometimes see pods of small (~4 ft) Spotted Dolphins here on the Silver Bank (in the Dominican Republic). The two species sometimes interact: the dolphins "tease" the whales, often mothers with calves. The dolphins dart in and out, and the humpbacks typically respond by slapping the water with their long pectoral fins along with other apparently agitated behaviours, seemingly trying to get the dolphins to leave them alone. This week we observed a completely different and suprising interaction.

We found a male juvenile whale (~20 feet long, perhaps 3 years old) logging on the surface. We put people in the water and he swam right up to everyone several times, very nice and easy. At some point 20 spotted dolphins appeared and the juvenile started slashing away at them, behaviour we normally expect to see. But after a few minutes Lorenzo Martinez - a Dominican whale expert and National Park official -remarked that the juvy (whale) was actually following the dolphins. The young whale followed the dolphins for perhaps 4-5 miles. Whenever we couldn't find the juvy, we would just look for dolphins, go to them and the juvy would show up. Toward the end, Captain Denise Lawrence put us in the water just as the the pod of dolphins was approaching our tender. I saw 10-15 scattered dolphins go by, then five dolphins in a tight pack, followed immediately by the juvenile humpback whale.

Shortly afterwards, this remarkable inter-species interaction ended. A mother, calf and their adult male escort swam nearby. Our juvenile whale attempted to join the group, but the escort manuvered between the juvenile and the mother and calf, rolled onto his side and repeatedly slammed the water with his tremendous pectoral fin, warning the juvenile to stay away.

Tom Conlin, whale naturalist and our host on the Silver Bank, has been observing the humpbacks and dolphins here for nineteen years. He told us that we had been very lucky to see this dolphin-whale encounter which, from his experiences with cetaceans, is probably quite rare.

Friday, March 13, 2009

Silver Bank 2009

I'm back again on the Silver Bank in the Dominican Republic with the humpback whales and Tom Conlin of Aquatic Adventures, aboard the Nekton Rorqual. Artist Gregory Colbert and his crew were on board for the last ten days filming free divers with the whales. They created some beautiful images, the divers and whales sometimes appeared to be falling together through outer space.