The seafloor is the final resting place for much of the materials washed into the ocean from land, for minerals forming in the ocean, and for detritus from organism that once populated the sunlit surface ocean. But the exchange between the seafloor and the overlying water column is not a one-way process. Once the material settles on the seafloor it is often subjected to intense biological reworking and recycling. Some of this recycled substrate makes it back into the water column, and if it is picked up by upwelling currents it might even be returned to the sunlight surface to once again supply nutrients to the biota, completing the cycle. The exchange the between the water column and the seafloor is especially important in the shallow waters of the highly productive coastal oceans. In our department we study the environmental controls of this bi-directional exchange process and linkages between biology and chemistry.
Why is the sea salty? That’s probably the first chemistry question we ask our students in Introduction to Oceanography. Some ancient folk tales will have you believe that the source of the salt is a magic mill that was accidentally dropped on the bottom of the sea where it continues to crank out salt. Turns out there is some truth to these folk tales, only that the ‘magic mill’ is on land, not in the ocean. Mountains are ground down to a fine powder through a grab bag of processes we collectively refer to as weathering. What is left of the rocks is washed into the sea and makes it salty. Weathering is only one of the many reasons why marine chemistry and geology are inextricably linked. Nutrients and carbon often enter the ocean from land, as well as being formed in the ocean itself. Their distribution determines where in the ocean biology can thrive and in turn, their uptake and use by organisms impacts their distributions. The ocean contains 50 times more carbon than the atmosphere, owing to the ease with which CO2 reacts with water and therefore plays a vital role in absorbing much of the anthropogenically produced CO2. But the ocean’s capacity to absorb this ‘surplus’ carbon is not limitless, and the addition of CO2 can be harmful to some organism such as corals. The sediments are the ultimate resting place for anything that enters the ocean, after it has been churned over countless times by chemical, physical and biological processes. Who would have thought that we can learn from old folk tales and fables—Hansel & Gretel anybody?
Coastal & Estuarine Processes