Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
• Data Files
• Supplemental Files
• Related Publications
• Related Datasets
• Parameters
• Instruments
• Deployments
• Project Information
• Funding

These data are published in Hirsh et al., see related publications section.

The moorings were deployed from June to October 2018. The moorings consisted of a subsurface mooring buoy anchored to a weight so that it was approximately 1 m below the surface at spring low tide. A 5 m line connected the subsurface buoy to a small float at the surface.

Inside Kelp Forest Mooring Instruments:

• 3 MiniDO2T dissolved oxygen loggers (Precision Measurement Engineering (PME), 5 minute sampling  frequency)
• 3 SBE 56 thermistors (Sea-Bird Electronics, 1 minute sampling frequency)
• 2 HOBO Pro v2 temperature loggers (Onset Data Loggers, 1 minute sampling frequency)
• 1 HOBO U20L pressure sensor (Onset Data Loggers, 1 minute sampling frequency)
• 1 miniPAR sensor (PME, 1 minute sampling frequency). PME miniPAR sensors were paired with PME miniWIPERs set to wipe the PAR sensors every six hours to prevent biofouling.
• 7 pH loggers were deployed on the kelp mooring between July and October. The kelp mooring configuration included two SeapHOx instrument packages (Bresnahan et al., 2014) deployed 1 meter above the bottom (mab) and just below the subsurface mooring buoy. Each SeapHOx consisted of a Honeywell Durafet pH electrode (Martz et al., 2010), an Aanderaa 4835 oxygen optode, and an SBE-37 MicroCAT CTD equipped with a pressure sensor. The other 5 pH loggers (mFETs) were custom built at the Monterey Bay Aquarium Research Institute utilizing Honeywell Durafet electrodes (Martz et al., 2010). SeapHOxes measured pH, O2, temperature, salinity and pressure every 10 minutes, whereas mFETs measured pH and temperature every 5 minutes.
• An SBE 37-SM MicroCAT CTD recorder was deployed at mid depth on the mooring beginning in mid-August with sampling frequencies of 5 minutes.
• A miniDO2T sensor was installed on a surface buoy located ~50 m from the kelp mooring between July 18 and August 1. This two-week miniDO2T deployment provided the only in situ surface O2 data inside the kelp forest.

Outside Kelp Forest Mooring Instruments:

• 3 MiniDO2T dissolved oxygen loggers (Precision Measurement Engineering (PME), 5 minute sampling  frequency)
• 3 SBE 56 thermistors (Sea-Bird Electronics, 1 minute sampling frequency)
• 2 HOBO Pro v2 temperature loggers (Onset Data Loggers, 1 minute sampling frequency)
• 1 HOBO U20L pressure sensor (Onset Data Loggers, 1 minute sampling frequency)
• 1 miniPAR sensor (PME, 1 minute sampling frequency). PME miniPAR sensors were paired with PME miniWIPERs set to wipe the PAR sensors every six hours to prevent biofouling.
• 1 pH logger (mFET) was deployed between July and October and measured pH and temperature
  every 5 minutes. The mFET was custom built at the Monterey Bay Aquarium Research Institute
  utilizing Honeywell Durafet electrodes (Martz et al., 2010).
• An SBE 37-SM MicroCAT CTD recorder was deployed at 13.5 man beginning in mid-August with
  sampling frequencies of 5 minutes.

Calibration by taking discrete samples alongside sensors in situ can lead to relatively large uncertainties, especially in highly dynamic coastal environments (Bresnahan et al. 2014); therefore, we decided to calibrate sensors in a flow through tank where the pH is more stable, and multiple discrete samples for DIC and TA analysis could be collected. Prior to deployment, the mFET sensors logged in a tank for 6 days (3 discrete samples) and the SeapHOxes logged in an adjacent tank for 1 day (2 discrete samples). We estimate the accuracy of the pH sensor data to be ± 0.015.

Oxygen sensors were calibrated by making measurements in a black bucket filled with freshwater while bubbling air for 8 hours. We assumed 100% saturation and applied a gain correction to the raw sensor output (Bittig & Körtzinger, 2015; Bushinsky & Emerson, 2013; Johnson et al., 2015). Because the air-stone was placed at the bottom of the bucket,  elsewhere we would expect slight over-saturation. However, since the depth of the bucket was < 40 cm, we estimate the accuracy of this calibration to be better than 1-2%. Post-deployment calibration indicated no drift in the oxygen sensors.

Sensor data were quality controlled with several steps. First, obviously erroneous data such as spikes were removed. When bubbles were present on the sensors they led to clearly erroneous data; for instance, pH values typically changed in a large, stepwise manner (usually >0.3 or more) with no correlation to temperature or O2.

Second, the sensors were deployed facing downwards on the mooring line, and bubbles from divers were sometimes trapped on the sensing surface for several hours, leading to incorrect sensor readings. The data bias by bubbles was clearly evident. Sensor data that showed short, stepwise shifts when divers were near the mooring were manually removed.

Finally, the first day of sensor data is not included in this data set to ensure that the instruments were fully equilibrated with environmental conditions.

BCO-DMO Processing notes:

• Adjusted column headers to comply with database requirements
• Converted Timestamp to ISO format, and timezone from Pacific Standard Time (PST) to UTC

NSF Award Abstract:
Kelp forest ecosystems are of ecological and economic importance globally and provide habitat for a diversity of fish, invertebrates, and other algal species. In addition, they may also modify the chemistry of surrounding waters. Uptake of carbon dioxide (CO2) by giant kelp, Macrocystis pyrifera, may play a role in ameliorating the effects of increasing ocean acidity on nearshore marine communities driven by rising atmospheric CO2. Predicting the capacity for kelp forests to alter seawater chemistry requires understanding of the oceanographic and biological mechanisms that drive variability in seawater chemistry. The project will identify specific conditions that could lead to decreases in seawater CO2 by studying 4 sites within the southern Monterey Bay in Central California. An interdisciplinary team will examine variations in ocean chemistry in the context of the oceanographic and ecological characteristics of kelp forest habitats. This project will support an early career researcher, as well as train and support a postdoctoral researcher, PhD student, thesis master's student, and up to six undergraduate students. The PIs will actively recruit students from underrepresented groups to participate in this project through Stanford University's Summer Research in Geosciences and Engineering (SURGE) program and the Society for Advancement of Hispanics/Chicanos and Native Americans in Science (SACNAS). In addition, the PIs and students will actively engage with the management community (Monterey Bay National Marine Sanctuary and California Department of Fish and Wildlife) to advance products based on project data that will assist the development of management strategies for kelp forest habitats in a changing ocean.

This project builds upon an extensive preliminary data set and will link kelp forest community attributes and hydrodynamic properties to kelp forest biogeochemistry (including the carbon system and dissolved oxygen) to understand mechanistically how giant kelp modifies surrounding waters and affects water chemistry using unique high-resolution measurement capabilities that have provided important insights in coral reef biogeochemistry. The project sites are characterized by different oceanographic settings and kelp forest characteristics that will allow examination of relationships between kelp forest inhabitants and water column chemistry. Continuous measurements of water column velocity, temperature, dissolved oxygen, pH, and photosynthetically active radiation will be augmented by twice-weekly measurements of dissolved inorganic carbon, total alkalinity, and nutrients as well as periods of high frequency sampling of all carbonate system parameters. Quantifying vertical gradients in carbonate system chemistry within kelp forests will lead to understanding of its dependence on seawater residence time and water column stratification. Additional biological sampling of kelp, benthic communities, and phytoplankton will be used to 1) determine contributions of understory algae and calcifying species to bottom water chemistry, 2) determine contributions of kelp canopy growth and phytoplankton to surface water chemistry, and 3) quantify the spatial extent of surface chemistry alteration by kelp forests. The physical, biological, and chemical data collected across multiple forests will allow development of a statistical model for predictions of kelp forest carbonate system chemistry alteration in different locations and under future climate scenarios. Threshold values of oceanographic conditions and kelp forest characteristics that lead to alteration of water column chemistry will be identified for use by managers in mitigation strategies such as targeted protection or restoration.