From - Mon Jul 27 08:33:39 1998 Path: news.tamu.edu!news.sgi.com!nntprelay.mathworks.com!nntp-out.monmouth.com!newspeer.monmouth.com!nntp2.dejanews.com!nnrp1.dejanews.com!not-for-mail From: dmorgan@scires.com Newsgroups: sci.geo.geology,sci.geo.oceanography Subject: Re: Strange Cold Water Date: Wed, 22 Jul 1998 13:54:49 GMT Organization: Deja News - The Leader in Internet Discussion Lines: 156 Message-ID: <6p4qv9$h50$1@nnrp1.dejanews.com> References: <35b0ca10.144020565@news.magiclink.com> NNTP-Posting-Host: 209.54.236.83 X-Article-Creation-Date: Wed Jul 22 13:54:49 1998 GMT X-Http-User-Agent: Mozilla/4.05 [en] (Win95; I) Xref: news.tamu.edu sci.geo.geology:57468 sci.geo.oceanography:9126 Interesting that somebody actually HAS seen something like this before, and that it occurs in conjunction with dry years, and that it is a coastal phenomenon. How's this for an explanation: Suppose that the wind driven currents in this area take a net amount of water away from shore. Any w/nw wind might do this, with the Coriolis force pushing water south. Next, suppose in a normal year any offshore transport is balanced by water input from rivers in the area. This leads to two interesting possibilities: 1. The high pressure system bringing the dry weather to the region also brings winds that increase the volume of water moved offshore. 2. The volume of water transported offshore cannot be balanced by input from rivers in the area. Either one or both of these possibilities change the water balance and could provide the force necessary to bring heavy, cold water up from the deep offshore waters. Any physical oceanographers care to weigh in here? Another thing... I don't know what "clear, cold" water they are talking about. It might have been clear when they first observed it in May, but it's as thick as pea soup now. I went diving off Destin this weekend. Our first dive was in 85 feet of water about 4 miles offshore at the liberty ship "Thomas Hayward". The surface waters are fairly warm and relatively clear... probably mid 70's with 40' visibility. At about 30' down though you reach a strong thermocline and very turbid water, maybe 6' visibility. Around 45' deep the temperature evens out in the mid 60's and the visibility opens up to around 25' or so. We saw plenty of fish around the wreck at 80', but they did seem a bit sluggish. Our second dive was on the tug boat "Miss Louise" in 55' of water. Same story with the thermocline and visibility, but everything here was DEAD-- crabs, snails, clams, grouper, batfish, everything. It was pretty eerie. Okay here's another theory... (again totally unsubstantiated by real research) The cold upwelling waters don't need to be particularly low in oxygen when they come up. The surface waters in the gulf are normally fairly clear because plankton growth is limited by a lack of nutrients. Cold, deep waters, however, are generally high in nutrients, but pytoplankton can't grow down deep because there is not enough light. When these nutrient rich deep waters get brought up close to the surface though, the plankton can just take off, leading to water that looks like pea soup. Another thing is going on here. Since the water is colder than usual, and the weather has been hotter than usual, the thermocline is much stronger than usual. This serves to isolate the bottom waters from the surface, and from the normal supply of fresh oxygen from the surface. As all the new biological activity around and below the thermocline uses up oxygen, there is no source to replace it, so the dissolved oxygen levels in the bottom waters just drop and drop. This seems to fit with what I saw-- a fairly clear, warm upper layer of "normal" gulf surface waters, a turbid layer of high biological activity where oxygen and light from above and nutrients from below are available, a strong thermocline, and a clearer low-oxygen layer below. I'd really like to hear what some real oceanographers think. It seems like a very interesting phenomenon-- a great topic for a Masters or Ph.D.! Cheers, Doug Morgan In article <35b0ca10.144020565@news.magiclink.com>, hotater*@magiclink.com (Jack Belk) wrote: > On Fri, 17 Jul 98 16:01:47 GMT, jtornabene@centuryinter.net > (Joan Tornabene) wrote: > and a guy in Idaho answered: > I grew up along the Gulf coast of Fla. This is not unusual > for a drought year. I speculate it has something to do with > hot dry weather and a "turn over" of the Gulf much like > Northern lakes in the spring. > Jack Belk > > >Thursday, July 16, 1998; Knight Ridder Newspapers > >MIAMI -- A dramatic and mysterious cooling of waters in the northeast Gulf of > >Mexico is killing fish and chilling bathers along the beaches of the Florida > >Panhandle. > > Coastal water temperatures from near the Alabama line to as far east as > >Panama City, Fla., plunged suddenly from the upper 80s last week to the low 70s > >-- the kind of surf temperatures you might expect off Cape Cod this time of > >year. > > What is most puzzling to scientists is that the clear, cold water is devoid > >of life. Fish are smothering in its extraordinarily low levels of dissolved > >oxygen. > > "Nobody has ever seen anything like this before," said Gary Fitzhugh of the > >National Marine Fisheries Service in Pensacola. "And nobody has come up with > >an explanation about what's causing this phenomenon." > > The best scientific guess right now -- and it's just a guess -- is that the > >cold water has welled up from the DeSoto Canyon. The canyon's terraced walls > >begin their gradual descent to 6,000 feet just 30 or so miles off the Panhandle > >beaches. The canyon is believed to play an important role in steering the > >tropical Loop Current through the Gulf. > > "There's just not a whole lot known about the specifics of what goes on in > >that canyon," said Sneed Collard, a biological oceanographer at the University > >of West Florida. "So it's very hard to say why there would be an upwelling at > >this time." > > The chilly water -- with temperatures in the lower 60s a few miles off the > >Panhandle's beaches -- was first noticed by fisherman and divers in mid-May, > >Fitzhugh said. > > The U.S. Geological Survey saw it then too in satellite imagery. The cold > >water was stretched in a 15- to 20-mile wide band just a few miles off the > >beaches, he said. > > What was startling about that band was its utter lifelessness. > > "In 80 to 100 feet of water you would see only dead or lethargic fish and > >shrimp," Fitzhugh said. "We were being told all kinds of crazy things. There > >were reports of big fish, like big electric rays, in very shallow water where > >you would never see them. > > "It was like everything was being squeezed out ahead of this cold water." > > The water has extraordinarily low levels of dissolved oxygen that marine > >animals need. Gulf waters off Florida usually have dissolved oxygen that > >measures 4 or 5 milligrams per liter; oxygen levels in the cold water plume > >measured less than 1 milligram and as low as 0.2, said Nancy Rabalais, a > >Louisiana researcher considered an expert in the impacts of low levels of > >dissolved oxygen or anoxic conditions on marine animals. > > "That low reading is very surprising," Rabalais said. "Usually, cooler water > >brings oxygen with it." > > Not only should the cold water have carried larger amounts of dissolved > >oxygen, it should also not have been at the surface. It should have sunk. > > "Having cold water from top to bottom probably killed all the food sources > >for marine life," Collard said. > >--------------------------------------------------------------------- > > > >It sounds like the geologists haven't been there yet, they've only seen the > >satellite images. > > > >We have water like this in Ohio. There are a lot of rivers running underground > >through limestone in western Ohio. This water is cold and devoid of oxygen. > >There are many caves to tour that these underground rivers have carved. At the > >"Blue Hole", the water wells up to the surface and forms a large round pool. > >The streams coming off the Blue Hole have water wheels in them to aerate the > >water so they can raise trout there. > > > >Maybe some earth movement beneath the Gulf waters has released and pushed up > >this water??? Does anyone have any ideas? > > > >Joan Tornabene > >jtornabene@centuryinter.net > > > > > > Remove the * from the E-Mail address if one is there > -----== Posted via Deja News, The Leader in Internet Discussion ==----- http://www.dejanews.com/rg_mkgrp.xp Create Your Own Free Member Forum