Chelsea Rochman Challenger Assignment ok for web Levin SIO 277 Nov 1 2007 The Discovery of Life in Oxygen Deprived Waters Before the Challenger Expedition the deep sea was thought to be devoid of life The Azoic Hypothesis in 1859 stated that the deep sea is dark cold high pressure stagnant and anoxic We now know that some of this hypothesis is correct the deep sea is dark cold and has high pressure However we also know that there is plenty of life in the deep and that it is not stagnant or anoxic Even in areas where oxygen is scarce it is certainly not devoid of life The H M S Challenger Expedition took place from 1872 1876 with C Wyville Thomson as its leader One of the objectives of the trip was to look at the distribution abundance and origin of deep sea organisms The Challenger disproved the Azoic Hypothesis by discovering that there is abundant life everywhere This cruise proved that there was life in the deep sea below 550m however they did not prove that there was life everywhere The naturalists aboard the Challenger believed that there is no life where oxygen concentrations were low In the Challenger reports it is written that in the Black Sea now so also was there in all likelihood in Paleozoic times insufficient O2 in deep water to support a deep sea fauna While we do know today that the Black Sea is the world s largest body of anoxic water we also know that this does not necessarily mean that there is no life found there We now know that anaerobic oxidation of methane occurs in the deep sea as a substitute for oxygen Methane consuming archaea are found in the deep anoxic zone of the Black Sea There are also sulfate reducing bacteria found in the deep waters of the Black Sea Stuart et al 2002 Animals have evolved adaptations in order to survive in anoxic waters these adaptations remained undiscovered at the time of the Challenger Expedition The Challenger proved that there was life in the deep and they also realized that there were oxygenated waters below 550m They understood that in the Mesozoic as the water cooled that the colder water was dense and sunk The cool sinking water brought oxygen to the deep sea However the reports states that this cooling event was what made life in the deep sea possible for the first time The Challenger Expedition did travel 68 890 nautical miles and did visit 362 stations however they did not come upon what we now call an Oxygen Minimum Zone If they had they would have realized that fauna can thrive where oxygen concentrations are low and have adaptations in order to do so Below is a map of the route of the Challenger and below that is a map of the world s Oxygen Minimum Zones Route of the H M S Challenger By comparing the two one can see that the H M S Challenger did not sample in any of these zones The discovery of Oxygen Minimum zones was not until 1925 when the Meteor Expedition set out from Germany to measure the ocean s depth study marine chemistry and on the side extract gold from seawater As we know the ship did not succeed on extracting gold but they did find a wedge of oxygen deficient water 300 400 meters down off Southern Africa Levin 2002 Oxygen Minimum Zones or OMZs are like the name implies areas in the ocean where the oxygen concentration is low below 0 5ml L Oxygen minimum zones are extensive stretches of sea floor exposed to permanent severe oxygen depletion Levin 2003 They are generally found at bathyal depths 200 1000m OMZs occur in areas where oceans experience a combination of high productivity induced by upwelling and limited mixing that leads to development of oxygen depletion Kamykowski and Zentara 1990 In an OMZ site there is a large flux of nutrients to the deep sea because the water column above does not support enough life to consume all of these materials thus the sea bed below OMZs receive higher inputs of organic matter from the productive overlying waters Levin 2003 Within these sites there is not only plenty of food but less predation from animals that are intolerant of low oxygen Because of this it makes sense that animals would develop adaptations to tolerate low oxygen It provides a refuge for animals to flee from predation While some animals will use the OMZ as a temporary refuge others live their entire lives OMZs benefitting from the abundant food and lower predation While the OMZs may have a lesser density of fauna then oxygenated waters they certainly do support a significant amount of fauna that have adapted to thrive in these environments Some of the adaptations that organisms have acquired in order to increase the effectiveness of oxygen uptake are raised ventilation rates increased efficiency of oxygen removal from the bloodstream elevated circulation capacity increased gill surface area reduced blood to water diffusion distances and increased blood pigment affinity for oxygen Childress and Siebel 1998 OMZ sediments also characteristically support dense populations of bacteria that can store and use nitrate as an electron acceptor for sulphide oxidation Levin 2003 Organisms that live in OMZs that have a calcareous test usually will be smaller with a porous test Having a smaller size enhances the surface area to volume ratio in order to facilitate respiration The pores in their tests will also facilitate oxygen exchange because mitochondria are more abundant near pores Levin 2003 Other than lower density trends in macrofaunal community structure are lower biomass decrease in species richness raise in dominance and decrease in individual body size with a decrease in oxygen Polychaetes tend to be the most abundant class within the communities of OMZs Examples of these trends can be seen in various papers On the Peru margin there were distinct patterns of decreasing macrofaunal abundance and diversity with decreasing oxygen The majority of the fauna were a part of the class Polychaeta Levin et al 2002 On the Oman continental slope in the NW Arabian Sea the species richness was remarkably low and the dominance was high The fauna also consisted primarily of polychaetes Levin et al 1995 These are only a couple of results from the many papers now published on what we now call OMZs Since the discoveries of the Meteor Expedition the need to learn more about OMZs has become increasingly important Ecological problems associated with the occurrence of low oxygen are increasing on a global scale The occurrences of OMZs appear to be increasing in shallow coastal and estuarine areas most likely