Whole‐Ocean Changes in Silica and Ge/Si Ratios During the Last Deglacial Deduced From Long‐Lived Giant Glass Sponges

Silicon is a keystone nutrient in the ocean for understanding climate change because of the importance of Southern Ocean diatoms in taking up CO2 from the surface ocean-atmosphere system and sequestering carbon into the deep sea. Here we report on silicon isotopes and germanium-to-silicon ratios in giant glass spicules of deep-sea sponge Monorhaphis chuni over the past 17,000 years. In situ measurements of Si isotopes and Ge concentrations show systematic variations from rim to center of the cross sections. When calibrated against seawater concentrations using data from modern spicule rims, sponge data indicate that dissolved silica concentrations in the deep Pacific were similar to 12% higher during the early deglacial. These deep Pacific Ocean data help to fill an important global gap in paleo-nutrient records. Either continental sources supplied more silica to the deglacial ocean and/or biogenic silica burial was lower, both of which may have affected atmospheric CO2.