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Relationship Between the Concentration of Atmospheric Carbon Dioxide and the pH Levels in Oceans

Info: 2781 words (11 pages) Essay
Published: 18th May 2020 in Environmental Sciences

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Title:What is the relationship between the concentration of atmospheric carbon dioxide and the pH levels in oceans?

Claim: Humans have changed the chemistry of the oceans.


Ocean acidification has a become a global issue that majorly effects shellfish; which, therefore effects the ocean food chain, food supplies for humans and the fishing industry. Shelled animals (mollusk) such as mussels, oysters, clams and starfish produce calcium carbonate shells (Fitzer, 2019). Through acidification if the amount of carbonate available is reduced, it limits the capability of these species to create shells (Fitzer, 2019). These organisms are on the bottom of the food web and reduction in these species can cause a ripple effect throughout the whole food web (Dien,2013). A study conducted in 2015 by Oregon State University revealed, areas such as Pacific Northwest, Massachusetts and Gulf of Mexico who are dependent on the 1 billion mollusc industry are in a long term economic risk the rise of ocean acidification (Oregon State University,2015).

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Humans is defined as a “bipedal primate mammal (Homo sapiens)”  (Merriam-Webster, 2019). As well, changed is defined as “to make the form, nature, content, future course, etc., of (something) different from what is or what it would be if left alone” (THE AMERICAN HERITAGE IDIOMS DICTIONARY, 2002). For the purpose of this investigation, Human will include people and how their actions and activities increase the amount of anthropogenic carbon dioxide in the atmosphere and cause a change from the original state of an oceans chemistry. Activities include: transport usage, manufacturing, agriculture and the use and burning of fossil fuels (Climate Change in Australia, 2016). Anthropogenic carbon dioxide is “(chiefly of environmental pollution and pollutants) originating in human activity” (Lexico,2019). The change can be identified by the pH of the ocean. A pH scale is used in order to identify the pH of a substance; the scale ranges from 0 to 14 and is used to measure how acidic or basic a substance is (CeNCOOS,2018). The pH scale is a logarithmic index and a small decrease in pH represents a large increase in acidity (CeNCOOS,2018).  The pH of ocean surface waters has already dropped from 8.16 to 8.05 from the beginning of the industrial revolution; and is predicted to drop 0.4 units by 2100 (CeNCOOS,2018).

To investigate the claim, the term chemistry is referring to “the composition and chemical properties of a substance” (Merriam-Webster, 2019). Ocean is defined as “a very large expanse of sea” (Lexico,2019). For the purpose of this investigation the way the oceans chemistry is changing  is though ocean acidicfication. Ocean acidification occurs when carbon dioxide gas is absorbed by the ocean and reacts with the seawater to produce acid (CeNCOOS,2018). The reaction between water and carbon dioxide is:


in water carbonic acid splits to produce a bicarbonate ion and release a hydrogen ion:


(CeNCOOS,2018). The greater the concentration of hydrogen ions the more acidic the ocean becomes.

Research Question: What is the relationship between the concentration of atmospheric carbon dioxide and the pH levels in oceans?

Analysis and Interpretation:

This research investigation will analyse 1 study from N. Bates, M. Best, K. Neely, A. Dickson and R. Johnson (2012) and 1 piece of evidence from Dr Pieter Trans and Dr David Karl (n.d.). The results from this study and piece of evidence will be used to ascertain if there is a relationship between concentration of atmospheric carbon dioxide and pH levels in oceans

Bates et.al (2011) aimed to investigate the relationship between the increase of anthropogenic carbon dioxide and ocean acidification in the North Atlantic Ocean. The methods used in this study is Seawater carbonate sampling at the Bermuda Atlantic Time- series study (BATS), sampling frequency, manometric methods and coulometric methods. For the purpose of this investigation data (D) and (E) are only going to be analysed.

Figure 1: A time series  showing the trend between (D)  Seawater pCO₂(partial pressure of carbon dioxide)  (purple symbol) and (E) surface water pH (orange symbol) and from 1984 to 2012 in the North Atlantic ocean (Bates, Best, Neely, & Johnson, 2012).

The results in Figure 1 show the relationship between the pCO₂ and pH in the North Atlantic Ocean between 1984 and 2012. The results indicate that as the time increases from 1984 to 2012 the amount of pCO₂ increases whereas, the pH decreases and become more acidic. The data for both the pCO₂ and pH have quite a few anomalies but both have a steady line of best fit. The pCO₂ is increasing from -25 μatm to 25 μatm and the pH is decreasing from around 0.03 to -0.03.

Dr. Pieter Trans and Dr. David Karl (n.d.) aimed to investigate the atmospheric carbon dioxide relationship in Mauna Loa with the Aloha seawater pCO₂ and pH; using a time series. This data has been formulated by the separate working and research from Dr. Pieter Trans and David Karl.

Figure 2: Time series of atmospheric CO2

at Mauna Loa (ppm) and seawater pCO2

and pH ( µatm

) in an Ocean station (ALOHA) in the North pacific ocean  from 1958 to 2018(Trans & Karl, n.d.).

The results in Figure 1 shows the relationship of a time series of atmospheric CO2

, seawater pCO2

and pH in the North Pacific from 1958 to 2018. It can be seen that there is a consistent increase of atmospheric  CO2

from around 320ppm to around 412.5 ppm from 1958 to 2018 and around 1988 the pCO2

in the seawater is consistent with the atmospheric CO2

; and is increasing. Also around 1988 the pH of the seawater is decreasing from around 0.02 units per 12 years. Therefore, it can be seen that as atmospheric  CO2

increases the pCO2

also increases and the pH decreases.

In response to the research question, it can be seen from the evidence presented in both Figure 1 and 2 that the relationship between concentration of atmospheric carbon dioxide and the pH levels in oceans is that as the concentration of atmospheric carbon dioxide increases the pH levels in oceans decrease.

The first limitation of the evidence was seen in the time series of the atmospheric CO2 

seawater pCO2

and pH in the North Pacific (figure 2). The data itself is formulated by two different sources, authors ,the Mauna Loa CO2

data was obtained by the National Oceanic and Atmospheric Administration Earth System Research Laboratory(NOAA) and the Aloha data was obtained in the University of Hawaii. This effects the sources credibility and reliability as the two authors have researched and worked on separate studies and have no connection. Therefore, it leaves room for any uncertainties and limitations in the data itself; as well as researchers may have used different methods within the study. The second limitation of the evidence was seen in figure 1. The data from figure 1 are subject to seasonal adjustment. Seasonal adjustment/ weighting is a method used to remove seasonal component in a time series that exhibits a pattern only seen in that seasonal time period (U.S. Bureau of Labor Statistics, 2001). The removal allows for a better analysis; therefore, the evidence not have the seasonal adjustment removed hinders the interpretation of the time series.


This research investigation sought to identify the relationship between the concentration of atmospheric carbon dioxide and pH levels in oceans. The evidence suggest a correlation between atmospheric carbon dioxide and decrease of pH levels as the concentration of C O2

increases the pH decreases; thus making the ocean more acidic.


In order to determine the quality of evidence the interpretation of the evidence and how up to date the data is will be discussed. Improvements to the research as well as extensions will be provided.

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The first issue with the quality of evidence was that interpretation of the data was very difficult. An improvement would be too make the scale wider spread and larger to accurately get an exact number from the data as well as making the line of best fit darker on the graph. This improvement would be beneficial as both data in figure 1 and 2 were very hard to read through the layout and scale. In figure 1 the data is very close together and the line of best fit was very hard to make out; as well it was hard to get an exact number from the data as the scale was very limited. Therefore, without the improvement the reliability and validity of this data is reduced.

Secondly, both of the evidence is not exactly up to date. An improvement would be too for both researches to conduct an up to date investigation as well as using the data already found to model what the future trends could look like. This improvement would be beneficial as figure 1 data only looks at the years 1984 to 2012 and figure 2 is from 1958 to 2018. With the rise of carbon dioxide in the atmosphere this allows researchers to keep on track how the pH levels of the oceans around the world is changing and provide more effective solutions to help the oceans.

An extension to the research would be to investigate other oceans around the world. To do this, researchers can investigate the Indian or Southern Ocean. This extension would allow researchers to investigate which ocean around the world pH is being effected by the increasing amount of carbon dioxide in the atmosphere. Another extension would be to investigate apart from the pH levels what other aspects of the ocean is changing due to human involvement. This can include temperature and would allow researchers to investigate if there are other critical issues that need to fixed and improved about the ocean. 

The evidence obtained in this investigation concludes that there is correlation with atmospheric carbon dioxide and pH levels and that as the atmospheric carbon dioxide increases, the pH levels decreases. Therefore, supporting the claim that humans have changed the chemistry of the oceans.


  • Merriam-Webster. (2019). Human definition. Retrieved from https://www.merriam-webster.com/dictionary/human
  • THE AMERICAN HERITAGE IDIOMS DICTIONARY. (2002). Change definition. Retrieved from https://www.dictionary.com/browse/change
  • Merriam-Webster. (2019). Chemistry definition. Retrieved from https://www.merriam-webster.com/dictionary/chemistry
  • Fitzer, S. (2019). The world’s shellfish are under threat as our oceans become more acidic. Retrieved from https://www.google.com/search?client=safari&rls=en &q=ocean+acidfication+effect+on+people&ie=UTF-8&oe =UTF-8
  • Dien, K. (2013). The Effects of Ocean Acidification on the Marine Food Chain. Retrieved from https://climateinterpreter.org/content/effects-oce an-acidification-marine-food-chain
  • Oregon State University. (2015). Threat of ocean acidification to coastal communities in US. Retrieved from http://www.sciencedaily.com/releases/2015/02/150223122604 .htm
  • Climate Change in Australia. (2016). GREENHOUSE GASES. Retrieved from https://www.climatechangeinaustralia.gov.au/en/cli mate-campus/climate-system/greenhouse-gases/
  • Lexico. (2019). Ocean. Retrieved from https://www.lexico.com/en/definition/ocean.
  • CeNCOOS. (2018). Ocean Acidification. Retrieved from https://www.cencoos.org/learn/oa/intro

       Lexico. (2019). Anthropogenic. Retrieved from https://www.lexico.com/en/definition/anthropogenic

  • Trans, P., & Karl, D. (n.d.). CO_2 time series in the North Pacific. Retrieved from https://www.researchgate.net/publication/228354388 _Ocean_acidification_of_the_North_Pacific_Ocean
  • Bates, N., Best, M., Neely, K., & Johnson, R., & Johnson, R. (2012). Detecting anthropogenic carbon dioxide uptake and ocean acidification in the North Atlantic Ocean. Retrieved from https://www.biogeosciences.net/9/2509/2012/bg-9-25 09-2012.pdf
  • U.S. Bureau of Labor Statistics., ,  (2001). What is seasonal adjustment? Retrieved from https://www.bls.gov/cps/seasfaq.htm


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