Cycles of nutrient trace elements in the Phanerozoic ocean

• LA–ICPMS analysis of marine pyrite outlines nutrient trace element trends in the Phanerozoic ocean
• Mo, Se, Cd, Tl and P all increase in concentration in the ocean by over an order of magnitude at 560–550 Ma.
• Cycles of trace elements indicate periods of nutrient-rich oceans followed by nutrient-poor oceans.
• Nutrient-rich oceans correspond with periods of high productivity and atmosphere oxygenation.
• Nutrient-poor oceans correspond with mass extinction events.

Availability of nutrients in the ocean can be a major factor affecting bioproductivity, burial of carbon and release of oxygen. However, the nutrient trace element (TE) composition of the palaeo-ocean cannot be measured directly. Here we present a comprehensive global dataset on the TE content of marine sedimentary pyrite in black shales, dating back 700 million years, and demonstrate a systematic cyclic evolution of pyrite TE composition with time. The nutrient TE, molybdenum, selenium, cadmium and thallium measured in pyrite, and phosphorus measured on whole rock, rise sharply at 560 to 550 Ma followed by several cycles of TE variation through the Palaeozoic and into the Mesozoic. A number of factors could explain the trends. We suggest that variations in continental uplift, erosion and nutrient flux rates were possible drivers of the oceanic nutrient cycles. The cyclic patterns through the Phanerozoic suggest periods of nutrient-rich oceans that fostered key evolutionary events, followed by nutrient-poor oceans that encompass several major mass extinction events.

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