Primary productivity and size structure of phytoplankton biomass on a transect of the equator at 135°W in the Pacific Ocean

Abstract. The geological record provides evidence for the periodic occurrence of water column anoxia and formation of organic-rich deposits in the North Atlantic Ocean during the mid-Cretaceous (hereafter called the proto-North Atlantic). Both changes in primary productivity and oceanic circulation likely played a role in the development of the low-oxygen conditions. Several studies suggest that an increased input of phosphorus from land initiated oceanic anoxic events (OAEs). Other proposed mechanisms invoke a vigorous upwelling system and an ocean circulation pattern that acted as a trap for nutrients from the Pacific Ocean. Here, we use a detailed biogeochemical box model for the proto-North Atlantic to analyse under what conditions anoxia could have developed during OAE2 (94 Ma). The model explicitly describes the coupled water, carbon, oxygen and phosphorus cycles for the deep basin and continental shelves. In our simulations, we assume the vigorous water circulation from a recent regional ocean model study. Our model results for pre-OAE2 and OAE2 conditions are compared to sediment records of organic carbon and proxies for photic zone euxinia and bottom water redox conditions (e.g. isorenieratane, carbon/phosphorus ratios). Our results show that a strongly elevated input of phosphorus from rivers and the Pacific Ocean relative to pre-OAE2 conditions is a requirement for the widespread development of low oxygen in the proto-North Atlantic during OAE2. Moreover, anoxia in the proto-North Atlantic is shown to be greatly influenced by the oxygen concentration of Pacific bottom waters. In our model, primary productivity increased significantly upon the transition from pre-OAE2 to OAE2 conditions. Our model captures the regional trends in anoxia as deduced from observations, with euxinia spreading to the northern and eastern shelves but with the most intense euxinia occurring along the southern coast. However, anoxia in the central deep basin is difficult to achieve in the model. This suggests that the ocean circulation used in the model may be too vigorous and/or that anoxia in the proto-North Atlantic was less widespread than previously thought.

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The effect of copper and manganese on phytoplankton in the Grand River (southern Ontario), Lake Erie and Pacific Ocean ecosystems

10.32920/ryerson.14643912 ◽

2021 ◽

Author(s):

Rachel Helen Welbourn

Keyword(s):

Pacific Ocean ◽

Food Webs ◽

Phytoplankton Biomass ◽

Lake Erie ◽

Natural Conditions ◽

Southern Ontario ◽

Cu Toxicity ◽

The Pacific ◽

The Pacific Ocean ◽

Grand River

With the increased use and loading of metals into the environment, the accumulation of toxic metals by phytoplankton has become a concern. Trace metal interactions with phytoplankton are of particular interest due to the influence of phytoplankton on the biogeochemical cycling of metals in aquatic systems. The study of the accumulation of metals and their toxicity in phytoplantkon is also of interest since phytoplankton lie at the base of many aquatic food webs. Toxic metals therefore have the potential to disrupt food webs and may have important implications on aquatic ecosystems. This study has chosen to focus on the response of phytoplankton to two trace metals in particular: copper (Cu) and manganese (Mn). Although both Cu and Mn are essential elements for phytoplankton, Cu is of particular interest as a toxicant. A number of laboratory studies have suggested that there exists a physiological interaction between Cu and Mn, and that Cu toxicity can be decreased in the presence of high concentrations of Mn. However, few studies have examined the effects of these metals on phytoplankton in their natural environments. The significance of this study is that it is one of the first to examine whether the importance of Cu toxicity and the interaction between Cu and Mn observed in the laboratory is also observable under natural conditions. Short-term bioassays were conducted in order to observe the response of phytoplankton from the Grand River (Southern Ontario) and Lake Erie to additions of various concentrations of eu and Mn under natural conditions. Similar long-term bioassay experiments were also conducted in the Pacific Ocean. Experiments in the Grand River and the Pacific Ocean revealed no significant decrease in phytoplankton biomass or in photosynthetic efficiency with the addition of various concentrations of Cu and Mn. In Lake Erie, phytoplankton biomass was only adversely affected following relatively high additions of Cu of 60 nM, and only under certain conditions. These results seem to indicate that under the tested conditions, Cu toxicity may not be of particular concern to the phytoplankton of the Grand River, Lake Erie and Pacific Ocean ecosystems.

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The effect of copper and manganese on phytoplankton in the Grand River (southern Ontario), Lake Erie and Pacific Ocean ecosystems

10.32920/ryerson.14643912.v1 ◽

2021 ◽

Author(s):

Rachel Helen Welbourn

Keyword(s):

Pacific Ocean ◽

Food Webs ◽

Phytoplankton Biomass ◽

Lake Erie ◽

Natural Conditions ◽

Southern Ontario ◽

Cu Toxicity ◽

The Pacific ◽

The Pacific Ocean ◽

Grand River

With the increased use and loading of metals into the environment, the accumulation of toxic metals by phytoplankton has become a concern. Trace metal interactions with phytoplankton are of particular interest due to the influence of phytoplankton on the biogeochemical cycling of metals in aquatic systems. The study of the accumulation of metals and their toxicity in phytoplantkon is also of interest since phytoplankton lie at the base of many aquatic food webs. Toxic metals therefore have the potential to disrupt food webs and may have important implications on aquatic ecosystems. This study has chosen to focus on the response of phytoplankton to two trace metals in particular: copper (Cu) and manganese (Mn). Although both Cu and Mn are essential elements for phytoplankton, Cu is of particular interest as a toxicant. A number of laboratory studies have suggested that there exists a physiological interaction between Cu and Mn, and that Cu toxicity can be decreased in the presence of high concentrations of Mn. However, few studies have examined the effects of these metals on phytoplankton in their natural environments. The significance of this study is that it is one of the first to examine whether the importance of Cu toxicity and the interaction between Cu and Mn observed in the laboratory is also observable under natural conditions. Short-term bioassays were conducted in order to observe the response of phytoplankton from the Grand River (Southern Ontario) and Lake Erie to additions of various concentrations of eu and Mn under natural conditions. Similar long-term bioassay experiments were also conducted in the Pacific Ocean. Experiments in the Grand River and the Pacific Ocean revealed no significant decrease in phytoplankton biomass or in photosynthetic efficiency with the addition of various concentrations of Cu and Mn. In Lake Erie, phytoplankton biomass was only adversely affected following relatively high additions of Cu of 60 nM, and only under certain conditions. These results seem to indicate that under the tested conditions, Cu toxicity may not be of particular concern to the phytoplankton of the Grand River, Lake Erie and Pacific Ocean ecosystems.

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