Ocean acidification variability in Kachemak Bay AlaskaKristine Holderied1, James Schloemer2, Kimberly Schuster1, Steve Baird2, Dominic Hondolero1

1NOAA / National Ocean Service/ National Centers for Coastal Ocean Science / Kasitsna Bay Laboratory 2Kachemak Bay National Estuarine Research Reserve / University of Alaska Anchorage

PROJECT HELP - Mike Geagel, Hans Pedersen & Connie Geagel at Kasitsna Bay Lab, Jacqueline Ramsay at Alutiiq Pride Shellfish Hatchery, & many KBNERR staffFUNDING - Exxon Valdez Oil Spill Trustee Council, Alaska Ocean Observing System, NOAA/NOS/NCCOSThis research was supported in part by the Exxon Valdez Oil Spill Trustee Council. However, the findings and conclusions presented by the authors are their own and do not necessarily reflect the views or position of the Trustee Council.

Thanks!

• Water quality station: Continuous (15 minute) oceanographic data from from near-bottom (~8 m depth) sensors at Kachemak Bay National Estuarine Reseach Reserve water quality station at Seldovia harbor (yellow star).

• Shipboard surveys: Monthly temperature/salinity data shown from vertical casts of conductivity-temperature versus depth (CTD) profilers during Kachemak Bay transect surveys (red lines, arrow for time series station). Carbon chemistry data are from water samples collected at surface and depth with a Niskin bottle. Analysis conducted with Burk-O-lator at the Alutiiq Pride Shellfish Hatchery.

Vertical profile time series of temperature (top) and salinity (bottom) from mid-Kachemak Bay CTD casts, 2012-2017.

Monthly relative freshwater content for Kachemak Bay calculated from CTD data on mid-bay transect

Coastal marine species and mariculture operations in the northern Gulf of Alaska have the potential to be adversely affected by ocean acidification, due to the presence of waters with low pH and low aragonite saturation. Kachemak Bay is located on the southeast side of Cook Inlet in southcentral Alaska. The bay has freshwater input from 15 glaciers and snowpack, an 8.7 meter tidal range, and intrusions of Alaska Coastal Current waters from the Gulf of AK shelf. The estuary experiences changes in pH and carbonate chemistry from upwelled shelf waters, from freshwater input associated with precipitation, glaciers and snowpack melt and from phytoplankton blooms. Seasonal, interannual and spatial variability in ocean acidification are being assessed in Kachemak Bay/Cook Inlet with oceanographic data from repeated small boat surveys and nearshore water quality stations.

Summary

pH from near-bottom sensor at Seldovia harbor station (2001-2018). Monthly average (black), maximum (red) and minimum (blue) values.

Data

•High frequency variations in Kachemak Bay estuary pH (daily to monthly time scales) are as great or more than seasonal and interannual changes.

•Ocean acidification conditions vary seasonally, with higher pH and aragonite saturation conditions in late spring and summer months, and under-saturation observed in fall months. Results are consistent with seasonal temperature patterns and increased freshwater input in late summer/early fall months.

•pH and aragonite saturation conditions were frequently, but not always, lower at depth than surface at a site. This reflects seasonal differences in mixing, freshwater input and shelf water intrusions.

KachemakBay

Alaska

Cook Inlet

Water column pH (top) and aragonite saturation (bottom) calculated from surface (blue) and deep (red) water samples at mid-bay (circle) and outer bay (triangle) stations.

Key Findings

Relative freshwater content calculated for mid-bay section from monthly CTD surveys (2012-2017). Note fresher conditions in fall months.

Results