Journal Article

Light Limitation of Poleward Coral Reef Expansion During Past Warm Climates

Brachert, T., Kruijt, A. L., Middelburg, J. J., Sluijs, A.

2024

Overview

The latitudinal range of modern shallow‐water tropical corals is controlled by temperature, and presently limited to waters warmer than 16–18°C year‐round. However, even during Cenozoic climates with such temperatures in polar regions, coral reefs are not found beyond >50° latitude. Here, we test the hypothesis that daily available solar radiation limited poleward expansion of coral reefs during warm climates, using a new box model of shallow marine coral calcification. Our results show that calcification rates start to decline beyond 40° latitude and drop severely beyond 50° latitude, due to decreasing winter light intensity and day length, irrespective of aragonite saturation. This suggests that light ultimately prohibits further poleward expansion in warm climates. In addition, fossil coral reef distribution is not a robust proxy for water temperatures and poleward expansion of reefs beyond 50° latitude is not an expected carbon cycle feedback of climate warming. Plain Language Summary Modern tropical coral reefs are found approximately between 30° north and south of the equator, where waters are warmer than 16°C year‐round. It is therefore often assumed that water temperature has the most important control on how far poleward we find tropical coral reefs. In the geological past, the earth has seen periods when global temperatures were much higher than they are today and oceans had tropical temperatures all the way to polar regions. However, tropical coral fossils were never encountered at these high latitudes. Rather, their distribution was restricted to latitudes below 50°N. Another important condition for tropical coral reefs to survive, is light availability. Toward the poles, winter day length and light intensity decreases significantly. We think that low winter day length limited coral reef growth and survival at high latitudes during these past warm climates. We test this with a computer model of coral growth and find that decreasing winter day length and light intensity cause coral growth to drop severely beyond 50°N. This result suggests that low light availability during winter months prohibited coral reefs from occurring at high latitudes during past warm climates. Key Points The uppermost latitudinal limit of tropical coral reefs was limited by winter daily available radiation during past warm climates Fossil coral reef distribution is not a robust proxy for water temperatures For the correct interpretation of coral reef records, coral‐light relationships need to be taken into consideration

• Publisher: John Wiley & Sons, Inc,John Wiley and Sons Inc
• Subject: Aragonite / Atmospheric Processes / Availability / Biogeochemical Cycles, Processes, and Modeling / Biogeochemical Kinetics and Reaction Modeling / Biogeochemistry / biogeography / Biogeosciences / Calcification / Carbon cycle / Cenozoic / Cenozoic climates / Climate / Climate change / Coral growth / Coral Reef Systems / Coral reefs / Corals / Cryosphere / Day length / Daylength / eocene / Equator / Fossils / Global Change / Global temperatures / Global warming / habitat modeling / Information Related to Geologic Time / Latitude / Light / Light intensity / light limitation / Luminous intensity / Macro‐ and Micropaleontology / Marine Geology and Geophysics / Marine invertebrates / Micropaleontology / Oceanography: Biological and Chemical / Oceanography: General / Oceans / Paleoceanography / Paleoclimatology / Paleoclimatology and Paleoceanography / Photoperiods / Polar environments / Polar regions / Research Letter / Solar radiation / Warm climates / Water temperature / Winter