Century-scale trends and seasonality in pH and temperature for shallow zones of the Bering Sea

• Published in: Proceedings of the National Academy of Sciences
• Main Authors: Fietzke, Jan, Ragazzola, Federica, Halfar, Jochen, Dietze, Heiner, Foster, Laura C., Hansteen, Thor Henrik, Eisenhauer, Anton, Steneck, Robert S.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2015
• Subjects: ocean acidification; boron isotopes; isotope imaging; laser ablation ICP–MS; crustose algae; /dk/atira/pure/core/subjects/biology; Biology; Bering Sea; Ocean acidification
• Online Access: https://doi.org/10.1073/pnas.1419216112; https://researchportal.port.ac.uk/portal/en/publications/centuryscale-trends-and-seasonality-in-ph-and-temperature-for-shallow-zones-of-the-bering-sea(e504e32e-542a-43e5-b63d-cb8e37efb83c).html; https://researchportal.port.ac.uk/ws/files/3260146/submitted_version_ATTU.pdf

No records exist to evaluate long-term pH dynamics in high-latitude oceans, which have the greatest probability of rapid acidification from anthropogenic CO 2 emissions. We reconstructed both seasonal variability and anthropogenic change in seawater pH and temperature by using laser ablation high-resolution 2D images of stable boron isotopes (δ(11)B) on a long-lived coralline alga that grew continuously through the 20th century. Analyses focused on four multiannual growth segments. We show a long-term decline of 0.08 ± 0.01 pH units between the end of the 19th and 20th century, which is consistent with atmospheric CO 2 records. Additionally, a strong seasonal cycle (∼0.22 pH units) is observed and interpreted as episodic annual pH increases caused by the consumption of CO 2 during strong algal (kelp) growth in spring and summer. The rate of acidification intensifies from -0.006 ± 0.007 pH units per decade (between 1920s and 1960s) to -0.019 ± 0.009 pH units per decade (between 1960s and 1990s), and the episodic pH increases show a continuous shift to earlier times of the year throughout the centennial record. This is indicative of ecosystem shifts in shallow water algal productivity in this high-latitude habitat resulting from warming and acidification.