How do sediments indicate changes in ocean productivity?

Sediments can reflect changes in ocean productivity primarily through their increased organic matter content. When ocean productivity is high, there is an increase in the growth of phytoplankton and other marine organisms, which subsequently die and sink to the ocean floor when they cease to exist or when they are consumed. This accumulation of organic matter contributes to the sedimentary layers at the ocean floor.

Higher levels of organic matter indicate that more biological activity has occurred in the water column, suggesting that the ocean was productive during that period. Such organic-rich sediments can be analyzed to assess past ocean conditions, including nutrient availability and overall productivity.

While sediments can also provide information through color changes or the presence of marine life, these indicators are more indirect compared to the direct association of organic matter content with biological productivity. Sediment temperature is not a reliable indicator of ocean productivity, as it reflects oceanic and climatic conditions rather than biological activity. Thus, the increase in organic matter content is a clear and direct indicator of changes in ocean productivity.