Ask an Explorer
Questions were sent to the science party during this expedition. Selected questions and answers are offered below.
Questions from: Augustine Kelly
Answers from: Andrew DeVogelaere, Huff McGonigal, Jim Barry, Chad King, and Lisa Borok
Are there tuna on the Davidson Seamount? Year round or seasonal? How big are they?
On this expedition, we haven't been studying the upper ocean where albacore live (in the top 50 meters of water). Albacore follow warmer temperatures along California in the fall and travel long distances around the Pacific seasonally. Albacore tuna are a popular recreational and commercial fishery along the West Coast, including the nearby ports of Morro Bay and Monterey Bay.
Are there Swordfish on the Davidson Seamount? Year round or seasonal? How big are they?
Yes, and a swordfish fishery operates in the surface and offshore waters of all of California, including the Davidson Seamount region. To learn about their size and seasons, we have a review of fisheries in the Sanctuary that can be downloaded.
You can also look up fishery information at the Pacific Fishery Management Council web site.
Are there rockfish on the Davidson Seamount? Year round or seasonal? How big are they?
We have not seen any rockfishes on the Davidson Seamount on this expedition, but we saw one thornyhead rockfish on our last NOAA/MBARI expedition into 2002. Our scientists could think of only two species in Central California that can reach the depths of 1,500 meters (4,920 feet). The shallowest peak on the Davidson Seamount is 1290 meters (4,192 feet), so rockfishes would only be found near the top (the bottom of the seamount is more than 3,300 meters, or 10,820 feet down).
Are there hot gas vents on the Davidson Seamount or any near by seamounts?
There are no hot vents off of the California Coast; the Davidson Seamount last erupted about 10 million years ago, so it's not currently an active volcano. However, we have seen lots of evidence of volcanic action from the past. We saw lava tubes in the "Big Valley" area, and there are lava boulders, called pillow basalts, everywhere. In Monterey Bay there are cold water seeps. These are caused by fluids beneath the seabed that leak out at places like scarps, faults, and slides.
Is there any quantity of rare minerals on these Seamounts? What are they?
Davidson Seamount was formed by volcanic eruptions more than 9.8 million years ago. As a result, most of the rocks here are basalts and other igneous (volcanic) materials. The surface of the old lava is coated with thin mineral layers, such as manganese crusts, that have precipitated out of seawater.
What is the water temperature on the bottom (at what depth?)?
Seawater temperature below a thousand meters (3280 feet) tends to be pretty constant and COLD! Today we took a reading of 1.6 ° C (about 34.8 ° F) at 2480 meters depth near the northeast end of the seamount. Be sure to check out our Mission Fact for more on temperature. You'll find the link at the bottom of our welcome page for this expedition:
http://www.oceanexplorer.noaa.gov/explorations/06davidson/welcome.html
Question from: Gabrielle Baumgartner, Science Teacher School of the Madeleine, Berkeley
My students and I are studying food webs. We are wondering if the sunlight does not reach down that deep, what are the organisms eating? Last year we learned about chemotrophic bacteria.
Answer from: Lisa Borok
Much of the deep sea appears to be fed by the "compost" from the upper sunlit portions of the sea. As plants and animals at the surface die and decay, they fall toward the seafloor, just like leaves and decaying material fall onto a forest floor.
We call this decaying material "marine snow" because it looks a little bit like white fluffy bits. In her 1951 book "The Sea Around Us," a famous ecologist, Rachel Carson, wrote that the dust and other material from the top of the ocean might fall to the depths "flake upon flake, layer upon layer – a drift that has continued for hundreds of millions of years… the material of the most stupendous "snowfalls" the Earth has ever seen." When Japanese scientists first described seeing the fluffy stuff from a submarine, they said it must be Miss Carson's "snow" and the name stuck.
Over the past 20 years or so, scientists have measured the amount of useable material in marine snow and found that there is plenty of carbon and nitrogen to feed many of the scavengers in the deep sea.
Many animals in the dark parts of the ocean filter marine snow from the water or scavenge it from the seabed. Carnivory is another very common lifestyle. Many animals have special lures to attract prey or have huge or flexible mouths to eat whatever comes along. As you've studied already, some organisms rely on bacteria for food, either by filtering it out of the water, grazing it off marine snow particles, consuming it in the sediments, or by hosting symbiotic bacteria in their tissues.
Question from: Pat Smith
I'm curious why lead 210 is used to age corals instead of another element.
Answer from: Allen Andrews
The reason lead-210 is used is because it is a naturally occurring radioisotope that is taken up by the coral skeleton. This isotope is specifically useful because it decays at a half-life of 22.26 years. Hence, it is useful for age determination up to about 120 years. Typically I trace the changes in lead-210 activity from the most recent growth to the oldest growth. If you take a look at the Coral Ageing essay on our Expedition website, there is a good description of the theory and application. So far I've had success with this technique for several species and hope to refine the estimates we have for bamboo coral.
Question from: Karen N.,
age 5, San Luis Obispo, CA
When did the volcano last erupt?
Answer from: Lisa Borok
The last time that Davidson erupted was about 9.8 million years ago! There's nothing active about this volcano right now, but the whole seamount is made up of old lava rocks. We're sending some neat photos of them back with our daily logs - check them out!
Question from: Robin Monti, Winter Springs, Florida, Rollins College
student
Have you seen much evidence of human-caused damage to the deep sea
corals you are studying this week, and if so, what type and to what extent?
Answer from: Huff McGonigal
While the Davidson Seamount is really a relatively pristine place, it is not out of reach of human influence. In our hours of exploring the seamount, we have found some trash on the seamount, like a coke bottle, a tin can, and a bucket. We've also came across a telecommunications cable that runs along the side of the seamount. Despite these isolated signs of humans, the habitat on the seamount is healthy and vibrant. The National Oceanic and Atmospheric Administration (NOAA) is considering including the Davidson Seamount as part of the nearby Monterey Bay National Marine Sanctuary. If this occurs, NOAA regulations will help ensure that the corals, sponges and fish on the seamount are protected from any future threats such as bio-prospecting, deep water trawling, and mineral extraction. Thanks for your question!
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