Southeast Alaska Long-term Seawater Monitoring Program for Ocean Acidification

Discussion

The seawater monitoring data demonstrates pH, total alkalinity (TA), and total dissolved inorganic carbon (TC) have prominent annual cycles. A gradient in carbon cycling exists between inside water and open ocean conditions (Fig. 6). Annual carbon cycles in water along the eastern Gulf of Alaska are about 10 times greater than cycles in the north central Pacific Ocean (Fig. 6). Temperature and salinity are considered major factors controlling the carbon cycles in seawater of Southeast Alaska. Oceanic seawater from the Gulf of Alaska drives salinity upward while freshwater input, both direct (precipitation) and indirect (terrestrial runoff), drives salinity downward. Indirect freshwater discharge from local rivers is a better predictor of salinity than precipitation (Fig. 7). The net result is a seasonal salinity oscillation. Therefore, salinity and temperature, which are easily and routinely measured, can be used to approximate pH, TA, and TC, and thus allow a broad spatial and temporal understanding of coastal and Southeast Alaska water conditions.

Annual variation in salinity, pH, TC, and TA declined with depth (0 to 25 m). Freshwater input (and mixing) exerts high control over carbon variation through dilution. Inside seawater is more alkaline (higher pH) when freshwater input is greatest in summer by terrestrial discharge. Freshwater alters alkalinity and the seawater buffering capacity among carbon species (CO2, CO3

2-, HCO3-, and H2CO3 and associated solids such as CaCO3). Biological

activity makes these chemical relationships even more complex by removal of CO2 from water in photosynthesis and removal of CO3

2- to form calcified structures in marine organisms.

The monitoring data can be used to understand how carbon cycles interact with indigenous fauna and flora. Phytoplankton blooms, as identified by chlorophyll-a concentrations in seawater, and an abrupt increase in pH suggest that plankton influence pH in inside water (Fig. 4). In theory, removal of dissolved carbon from water as plankton photosynthesize and grow should drive pH upward. In this study, as the plankton bloom advanced, calculated pCO2 concentrations dropped rapidly and water became more alkaline (pH increased). Several more seasonal observations will be necessary to substantiate (or refute) the hypothesis of phytoplankton influence in ocean acidification parameters of Southeast Alaska water.

The data presented herein primarily outlines the carbon chemistry of inside waters along the eastern shore of the Gulf of Alaska. The large seasonal carbon changes pose interesting biological questions for a wide variety of marine species indigenous to these waters. Have these organisms adapted to broadly variable conditions or have they developed behavioral strategies to avoid seasonal stresses? Is migration from acidic areas to more alkaline conditions undertaken, and if so even feasible for small plankton? How do shelled intertidal organisms deal with acidic events? Does (or has) this carbon cycle affected reproductive cycles, making early life stages more vulnerable? As the monitoring program continues, these and other questions are being considered to give insight into understanding the role ocean acidification will play in the seawater of Southeast Alaska.

ResultsSeasonal cycles in pH, TC, and TA occurred at all sample depths (surface to 25 m) in the water of Auke Bay, Lena Cove, and Favorite Channel (Fig. 3). The seawater was most basic during summer and most acidic during winter. The mean amplitude of the pH cycle in surface water was 0.600. The mean amplitudes for TA and TC in surface water were 896 and 1115, respectively. The TC and TA cycles are opposite the pH cycle.

Water temperature and salinity, the integrated outcome of solar and moisture cycles, heavily influence carbon cycles in water along the eastern Gulf of Alaska. Water temperature in inside water generally lagged photoperiod by about 1 month; salinity and temperature were roughly 0.5 year out of phase (Fig. 4). Linear fits between carbon parameters pH, TC, or TA (as dependent variables) and environmental variables salinity or temperature (as independent variables), were highly significant (P < 0.001; Fig. 5). Total alkalinity and TC were essentially in phase with salinity cycles; pH was in phase with temperature (Fig. 3 and 5).

Chlorophyll a concentrations in the water, an indicator of phytoplankton productivity, increased rapidly as light levels and water temperature increased in spring (Fig. 4). The pCO2 levels (estimated from pH and TC observations) decreased rapidly as the bloom increased and pH levels increased rapidly.

Carbon parameters, chlorophyll a, water temperature, and salinity were structured by depth (Fig. 3). Surface water tended to be more alkaline in the summer than deeper water (5 to 25 m); pH was about the same at all depths in winter (Fig. 3). Seasonal TA and TC fluctuations were similar to those of salinity with more surface fluctuation than deeper water (Fig. 3). Water temperature was about a degree cooler at depth than at the surface in summer and similarly warmer in winter.

No seasonal carbon cycles were evident in the freshwater stream, Auke Creek, located near the Auke Bay Marine Station for mean pH (7.296 ± 0.041), TA (267 ± 43 mol/kg), and TC (221 ± 9 mol/kg). Preliminary results from the Mendenhall River yielded similar results.

Project Overview

The Southeast Alaska Monitoring Program applies an ecosystem approach to develop baseline data and describe carbon cycles in coastal and inside water along the eastern margin of the Gulf of Alaska. The inside passage is a marine environment of frequent low pressure systems and high rainfall. Large barrier islands form a mountainous archipelago, partially separating inside water from open coastal water. Study sites were selected in the inside waters of southeastern Alaska near our laboratory in Juneau (Fig. 1). These Juneau sites have been sampled monthly for about 2 years and provide replicate measures of inside water. Two additional locations were recently added to the study to achieve a more comprehensive perspective of carbonate chemistry along the eastern Gulf of Alaska. One, added in May 2011, was established in Sitka Sound at the head of the Crescent Harbor (Sitka, Alaska) and at the margin of coastal gulf water (Fig. 1). The other location, added in August 2011, in Prince William Sound contains three sites, which are distributed to sample a range of inside to coastal water at the margin of the gulf (Fig. 1). Two freshwater sites are also monitored, Auke Creek and Mendenhall River, for the purpose of understanding how terrestrial runoff influences carbonate chemistry in inside waters.

This project seeks to understand how the rates and magnitude of ocean acidification will vary across time, space, and depth as a consequence of local and regional geochemical, hydrological, and biological mechanisms.

MethodsSeawater is collected monthly and every other month in Prince William Sound (PWS) following the sampling principles from the Guide to Best Practices for Ocean CO2 Measurements by Dickson, Sabine et al. (2009). Seawater is collected at varying depths (Fig. 1) using a Niskin sampler (Fig. 2) and then transferred to glass BOD bottles through a drawing tube fitted with a mesh sleeve (0.5 µm) to filter the seawater. Freshwater samples are collected directly into the BOD bottles. Actions are taken to keep the water samples free of air bubbles, such as sealing the BOD bottles with Apiezon-L grease. At the time of collection, the date, time, and temperature of the water are recorded for each sample.

Figure 2. Niskin water sampler (left) being deployed at Auke Bay Marine Station dock (right) to collect surface seawater.

The remaining unfiltered seawater in the Niskin sampler is transferred to Nalgene bottles for chlorophyll measurements. The chlorophyll samples are filtered (0.7µm) within 24 hours of collection, and the sample filters are placed in cryovials and stored in -80ºC freezers. The sample filters are processed by the Standard Acidification Technique and measured for chlorophyll-a concentrations by a fluorometer.

Four ocean acidification chemical analyses are run on the water samples following the standard operating procedures from the Guide to Best Practices for Ocean CO2 Measurements: pH, total alkalinity, total dissolved inorganic carbon, and salinity. Water samples are measured for pH by an Agilent UV/Visible Spectrophotometer using 10-cm cells and the indicator dye m-cresol purple. Water samples are measured for total alkalinity by the open cell titration method using a Mantech QC Titration Module with a TitraSip System and a 0.1M HCl-0.6M NaCl salt solution. Water samples are measured for total dissolved inorganic carbon by using a UIC CO2 Coulometer with Acidification Module plus 1.5 M phosphoric acid, potassium hydroxide (45%), and acidified potassium iodide (50%). Water samples are measured for salinity by a Guildline AutoSal.

For each analysis, quality assurance is incorporated in each batch of samples by including sample replicates for precision and a Certified Reference Material (CRM; Scripps Institution of Oceanography) for accuracy (≤5%).

Lawra Vanderhoof and Mark Carls Habitat and Marine Chemistry

Alaska Fisheries Science CenterNational Marine Fisheries Service

NOAAJuneau, Alaska

Lawra.Vanderhoof@noaa.gov

Figure 3. Annual pH, total alkalinity (TA), and total dissolved inorganic carbon (TC) cycles in inside waters of Southeast Alaska (means ± 1 standard error). Data were averaged among three sites (Auke Bay, Favorite Channel, and Lena Cove). Left-hand panels illustrate surface water; right-hand panels illustrate 7 to 25 m. Abscissa labels are month/year. The black curves indicate model predictions from temperature (pH) or salinity (TA and TC).

Figure 6. Annual carbon and salinity cycling in surface inside waters (0 to 0.5 m) of Southeast Alaska compared to surface open ocean conditions (0 to 10 m). Central Pacific Ocean data are from Station Aloha, Hawaii. Data are salinity (practical salinity units, psu), total alkalinity (TA), total dissolved inorganic carbon (TC), and pH. All parameters were measured directly in southeast Alaska (SEAK) coastal water; pH was estimated from TA and TC in the Aloha data set. All data are plotted on the same scales. Abscissa labels are month/year. Open ocean data were limited to the most recent two years of available data. Three seawater stations were combined for the SEAK data (means ± 1 standard error).

Fig. 5. Relationship between pH, TA, or TC and salinity or temperature. Open symbols identify surface samples and solid symbols indicate depth samples (7 or 25 m). Large circles identify first round outliers (plotted regression fits with 90% confidence bounds include these outliers and all other data).

Thank you to our co-workers (Dione Cuadra, Marissa Capito, Lawrence Schaufler, Larry Holland, Haley Poole, John Moran, John Thedinga) and partners from the Sitka Sound Science Center (Lisa Busch and Eric Matthes) for their constant teamwork and efforts in the past and future as this project continues.

The recommendations and general content presented in this poster do not necessarily represent the views or official position of the Department of Commerce, the National Oceanic and Atmospheric Administration, or the National Marine Fisheries Service.

Continuing Research

Continue monitoring the carbon parameters in local (inside) water through chemical analyses

Expand carbon data collection to a broader area of coastal water, so regional patterns and environments can be better compared

Continue monitoring phytoplankton activity as chlorophyll a production

Improve depth resolution down to 100 m to better describe depth structuring

Add the observation and measurement of dissolved organic carbon in seawater

Add atmospheric carbon monitoring to capture local conditions

Figure 4. Relationship among photoperiod, water temperature, and salinity in surface water (top panel) and pH, pCO2, and chlorophyll a (chla) in surface water (bottom panel). Data were averaged among three inside water sites (Auke Bay, Favorite Channel, and Lena Cove).

Figure 7. Relationship among freshwater precipitation in Juneau, freshwater discharge from Mendenhall River in Juneau, and salinity in surface seawater. Salinity data was averaged among three sites in Juneau (Auke Bay, Favorite Channel, and Lena Cove).

Figure 1. Map of Southeast Alaska seawater monitoring sites and depths at each location.

pH

Surface

7.600

7.800

8.000

8.200

8.400

TA

900

1300

1700

2100

2500

TC

900

1300

1700

2100

2500

Mid

9/09 5/101/10 1/11 9/115/119/10 9/09 5/101/10 9/111/11 5/119/10

Tem

pera

ture

(Cel

cius

)

Sal

inity

(psu

)

12

Pho

tope

riod

(h)

69/10 1/111/109/09 5/10

photoperiod

9

0109/115/11

temperature

20

5

salinity18

15

30 15

10

pCO

2 (u

atm

)

Chl

orop

hyll

a (u

g/L)

chla

9/110

9/09 1/115/101/10 9/10 5/11

10

20

07.600

200

4008.000

7.800

pH

pCO2

30

40

50

600

800

pH

8.200

8.400

10008.600

25

Men

denh

all d

isch

arge

(m^3

/sec

)

09/09 1/10

discharge

5/119/105/10 1/11 9/11

precip

75

50

125

100

Salinity

10

Sal

inity

(psu

)

20

30

9/07

TA

or

TC

(um

ol/k

g)

1800

1500

1200

2700

2400

2100

1/101/099/085/081/08

pH

9/095/09 9/09

Central Pacific Ocean (Aloha)

TC

TA

pH

9/111/119/105/10 5/11

8.000

7.800

7.600

Coastal water (SEAK)

8.400

8.200

Sal

inity

(psu

)

26

22

18

14

34

30

salinity

pH

7.600

7.800

8.000

8.200

8.400

TA (m

ole

/ kg)

900

1300

1700

2100

2500

TC (m

ole

/ kg)

Salinity (psu)10 15 20 25 30

900

1300

1700

2100

2500

Temperature (C)0 5 10 15 20

Auke BayFavorite ChannelLena CoveSitka SoundPWS insidePWS centralPWS entrance

Seawater Sites Surface 7 m 25 m 50 m 100 mAuke Bay Marine Station dock X X

Lena Cove X XFavorite Channel X X 70 m

Coghlan Island X X X 84 mSitka Crescent Harbor X X

PWS Port Gravina X X XPrince William Sound East X X X

PWS Cape Hinchinbrook X X XFreshwater Sites

Auke Creek XMendenhall River X

Southeast Alaska Inside Water at Favorite Channel, Juneau

Calcified Exoskeletons of Indigenous Biota of Southeast Alaska Seawater