Coccolith Sr/Ca is a robust temperature and growth rate indicator that withstands dynamic microbial interactions.

Area of Science:

• Marine Biology
• Paleoceanography
• Geochemistry

Background:

• Coccolithophores are vital calcifying microalgae with extensive fossil records.
• Organic proxies like U^K'₃₇ are influenced by algal-bacterial interactions, but inorganic proxies remain unstudied.
• Emiliania huxleyi, a key coccolithophore, interacts dynamically with bacteria, potentially affecting calcification.

Purpose of the Study:

• To investigate the impact of algal-bacterial interactions on coccolithophore calcification.
• To determine if bacterial presence alters inorganic coccolith Sr/Ca ratios, a proxy for productivity and sea surface temperature.
• To compare the robustness of inorganic versus organic paleo-proxies under microbial influence.

Main Methods:

• Culturing Emiliania huxleyi with and without associated bacteria.
• Quantifying coccolith cell coverage and overall calcite production.
• Analyzing coccolith Sr/Ca ratios in relation to environmental factors and bacterial presence.

Main Results:

• Bacteria preferentially attached to non-calcified algal cells.
• Coccolith coverage and calcite production were similar in cultures with and without bacteria.
• Coccolith Sr/Ca ratios were solely influenced by water temperature and algal growth rate, independent of bacterial interactions.

Conclusions:

• Coccolithophore calcification and calcite production are not significantly impacted by bacterial presence.
• The inorganic Sr/Ca ratio in coccoliths is a robust paleo-proxy, unaffected by microbial interactions.
• This highlights a key difference in the reliability of inorganic versus organic paleo-proxies in reconstructing past oceanic conditions.