Tuesday, March 23, 2010

"Oh, Behave!"

Did I mention that the ocean doesn’t always behave? We have spent years making measurements in the region around Los Angeles and Orange County along with our colleagues from the sanitation districts, USGS, SAIC, UCSD Scripps, etc. So we think we know the region pretty well. Last spring and this spring we have been flying robotic submarines called gliders (no propeller, see picture below) in the region between Seal Beach and Laguna Beach and offshore about 13 miles.

This vehicle doesn’t move quickly, only about 0.3 meters/second or about 0.6 knots. So if the speed of the ocean currents are very strong the glider can’t make the path that it’s supposed to fly. Up to now, we haven’t had a problem with this. But, ……. last week our glider started heading south toward San Diego at a speed of 1-2 knots, and we could not do anything to make it turn back. It was pointing north and heading south. The currents stayed high for the entire week. We had to chase the glider down to Carlsbad – we think it was hoping to have spring break in Mexico with all the other USC students. We were able to retrieve the glider before she crossed the border into Mexico, and will put it back out when the currents have subsided a bit.

Saturday, March 20, 2010

Coastal Upwelling

In the last blog we said we would talk more about harmful algal species, but what is happening in the ocean over the last couple of weeks is a process that contributes to the formation of some algal blooms, including some harmful species. If you live in southern California, you know that we experienced very strong winds out of the north to northwest last week. Strong winds like that are typical of the springtime, but are often weaker during El NiƱo years (like this year). But those were strong winds. What is the effect of those winds on the ocean?

We could discuss the more technical aspects of wind stress and wind stress curl and their effects on the upper ocean, or various processes that contribute to divergences in the ocean that result in upwelling of deeper water. But a simplistic explanation is that when the winds blow from the north along the west coast in the northern hemisphere they accelerate the nearsurface currents toward the south and because of the rotation of the earth these equatorward currents tend to veer offshore. As they veer offshore, water needs to come from somewhere to replenish the water that is moving away from the coast. The source of that water is generally from underneath the layer of water that moves offshore, and this water comes to the surface near the coast. Because deeper water is moving upward to the surface near the coast, we refer to the process as upwelling – vertical upward transport of the water (see the schematic below). The deeper water contains nutrients (nitrogen, phosphorus, and silicate) that support the growth of the microscopic plants (phytoplankton) in the ocean when they are exposed to sunlight. As a result when significant upwelling occurs along the coast, we often see a response in the growth of phytoplankton, just like we discussed when there is significant runoff from rain. While rain runoff is conducive the growth of a group phytoplankton called dinoflagellates, upwelling tends to support more conducive to a group of rapidly growing phytoplankton called diatoms.



In general, upwelling is a very positive process in the ocean. The cooler water is important for maintaining the livable climate of coastal California, and other regions of the world. The nutrients support a biologically productive coastal ocean ecosystem that provides California’s abundant sea life. It is also part of the process where the subsurface ocean ventilates to the surface and atmosphere.

We are in the process of seeing rapid phytoplankton growth along the Southern California Coast right now. However, one of the diatom species that is becoming abundant, Pseudonitzschia australis, can produce the neurotoxin domoic acid that can cause significant damage to the hippocampus region of the brain in mammals (including humans) and birds. Marine mammals and birds feed on the fish that consume these phytoplankton and as a result, we often see the effects when these animals show up on the beach. So far we haven’t seen a lot of the toxicity, but we are watching carefully to see if it develops. If you want to follow this, you can go the Harmful Algal Bloom web page maintained by the Southern California Coastal Ocean Observing System (http://www.sccoos.org/data/habs/index.php

Tuesday, March 9, 2010

It never rains in Southern California!

“It never rains in Southern California”1! At least it makes a good song.

It rained again this weekend. We are waiting for a good satellite image of the impacts of the event and should have one from today. So far this season 14.66 inches has been recorded at the National Weather Service’s (NWS) LA Downtown site.

One of the recent storms created a clear biological response in the ocean following the storm. As we mentioned in the previous posting on El Nino, runoff brings a lot of nutrients for plants (nitrogen, phosphorus, etc) into the ocean. Just as on land these plant nutrients promote plant growth, but the ocean plants are microscopic phytoplankton. Although microscopic, they are so abundant that they change the color of the water from blue to more greenish. The ocean color sensors on satellites detect these changes and enable us to measure the concentration of chlorophyll from the plants in the ocean. This enables us to measure the response of the upper visible ocean to the nutrient inputs from the rain runoff.

Between February 5 and 8 nearly 3.3 inches of rain was recorded at the downtown NWS site. That’s quite a bit of rain in a relatively short time. As a result there was a significant volume of runoff that went into the ocean. About 1 week after the rain event a significant phytoplankton response was observed from satellite with high concentrations in both Santa Monica Bay and San Pedro Bay south of LA/LB harbor, extending nearly halfway to Catalina Island (~10-12 miles). The two satellite images show the chlorophyll concentration a couple of days prior to the storm (top image) and the concentration about one week after the storm (bottom image). The large increase of chlorophyll between the two images shows the effects of the added nutrients from the runoff on the coastal concentrations of phytoplankton.




One of our research interests is not only that there are “blooms” of phytoplankton, but what species bloom, and under what conditions do they bloom. Some phytoplankton can produce toxins that are harmful to marine life, birds, and to humans if we consume shellfish or other fish that have eaten the toxic phytoplankton. To determine what species of phytoplankton are present we monitor the species of phytoplankton at various piers around southern California. Whether the runoff from land promotes the formation of toxic blooms is one question that we are addressing in our studies of these “harmful” blooms in southern California.

We’ll write more about that in the next installment.

Sources:
Rainfall information: National Weather Service - http://www.weather.gov/climate/index.php?wfo=lox

Satelliete Images: SCCOOS
http://www.sccoos.org/data/modis/modis_regions.php?r=3

1Hammond and Hazelwood, 1972.