14: Ocean Tides and Sea Level Rise
- Page ID
- 31583
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\(\newcommand{\avec}{\mathbf a}\) \(\newcommand{\bvec}{\mathbf b}\) \(\newcommand{\cvec}{\mathbf c}\) \(\newcommand{\dvec}{\mathbf d}\) \(\newcommand{\dtil}{\widetilde{\mathbf d}}\) \(\newcommand{\evec}{\mathbf e}\) \(\newcommand{\fvec}{\mathbf f}\) \(\newcommand{\nvec}{\mathbf n}\) \(\newcommand{\pvec}{\mathbf p}\) \(\newcommand{\qvec}{\mathbf q}\) \(\newcommand{\svec}{\mathbf s}\) \(\newcommand{\tvec}{\mathbf t}\) \(\newcommand{\uvec}{\mathbf u}\) \(\newcommand{\vvec}{\mathbf v}\) \(\newcommand{\wvec}{\mathbf w}\) \(\newcommand{\xvec}{\mathbf x}\) \(\newcommand{\yvec}{\mathbf y}\) \(\newcommand{\zvec}{\mathbf z}\) \(\newcommand{\rvec}{\mathbf r}\) \(\newcommand{\mvec}{\mathbf m}\) \(\newcommand{\zerovec}{\mathbf 0}\) \(\newcommand{\onevec}{\mathbf 1}\) \(\newcommand{\real}{\mathbb R}\) \(\newcommand{\twovec}[2]{\left[\begin{array}{r}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\ctwovec}[2]{\left[\begin{array}{c}#1 \\ #2 \end{array}\right]}\) \(\newcommand{\threevec}[3]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\cthreevec}[3]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \end{array}\right]}\) \(\newcommand{\fourvec}[4]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\cfourvec}[4]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \end{array}\right]}\) \(\newcommand{\fivevec}[5]{\left[\begin{array}{r}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\cfivevec}[5]{\left[\begin{array}{c}#1 \\ #2 \\ #3 \\ #4 \\ #5 \\ \end{array}\right]}\) \(\newcommand{\mattwo}[4]{\left[\begin{array}{rr}#1 \amp #2 \\ #3 \amp #4 \\ \end{array}\right]}\) \(\newcommand{\laspan}[1]{\text{Span}\{#1\}}\) \(\newcommand{\bcal}{\cal B}\) \(\newcommand{\ccal}{\cal C}\) \(\newcommand{\scal}{\cal S}\) \(\newcommand{\wcal}{\cal W}\) \(\newcommand{\ecal}{\cal E}\) \(\newcommand{\coords}[2]{\left\{#1\right\}_{#2}}\) \(\newcommand{\gray}[1]{\color{gray}{#1}}\) \(\newcommand{\lgray}[1]{\color{lightgray}{#1}}\) \(\newcommand{\rank}{\operatorname{rank}}\) \(\newcommand{\row}{\text{Row}}\) \(\newcommand{\col}{\text{Col}}\) \(\renewcommand{\row}{\text{Row}}\) \(\newcommand{\nul}{\text{Nul}}\) \(\newcommand{\var}{\text{Var}}\) \(\newcommand{\corr}{\text{corr}}\) \(\newcommand{\len}[1]{\left|#1\right|}\) \(\newcommand{\bbar}{\overline{\bvec}}\) \(\newcommand{\bhat}{\widehat{\bvec}}\) \(\newcommand{\bperp}{\bvec^\perp}\) \(\newcommand{\xhat}{\widehat{\xvec}}\) \(\newcommand{\vhat}{\widehat{\vvec}}\) \(\newcommand{\uhat}{\widehat{\uvec}}\) \(\newcommand{\what}{\widehat{\wvec}}\) \(\newcommand{\Sighat}{\widehat{\Sigma}}\) \(\newcommand{\lt}{<}\) \(\newcommand{\gt}{>}\) \(\newcommand{\amp}{&}\) \(\definecolor{fillinmathshade}{gray}{0.9}\)Long before clocks were invented, long before people were invented, and long before the first microbe snuggled up to a scalding vent of water, the Earth and the Sea heaved up and down at precise intervals, like clockwork. The heavings continue to this day, rising and falling, sometimes higher than the time before, sometimes lower, but timed to precision. Of course, we’re talking about daily changes in sea level—the theoretical height of the ocean at rest. The rising and falling occur as a result of the ocean tides—the changes in sea level caused by the gravitational forces of the Earth, Sun, and Moon.
The tides have existed since the moment that the Moon fell into orbit around the Earth, about 4.53 billion years ago, some 20 million years after the Earth gained most of its mass. Subsequently, organisms evolved adaptations and behaviors synchronized with the tides. They tolerate exposure to the air during low tides, when sea level reaches its lowest extent during the day. They carry out metabolic and reproductive activities when submerged during high tides, when sea level reaches its highest extent.
The tides also play a part in the everyday lives of people and have done so since antiquity. The Indians, Greeks, Romans, Babylonians, and Chinese described and predicted the tides. As early as 325 BCE, the height of the tides was proposed to depend on the phases of the Moon (Cartwright 2000). Tides made navigation of shallow seas perilous. Certain places were to be avoided at low tides. Swiftly rising tides created dangerous currents and ferocious whirlpools that could wreck an unsuspecting captain. The success of military operations in coastal waters hinged on the navigability of the waters and beaches at high or low tide.
Knowledge of tides assisted the hunting and gathering of seafood along shorelines, where abundant beds of oysters and mussels, or buried clams, might be found at low tide. The people of the Republic of Palau in the western North Pacific express their relationship with the tides in this way:
The rhythm of our life is the rhythm of the sea. We are born on a certain tide; we die on another. The tide carries our boats out to the fish and brings us back to feed our families. The seasons of our lives depend on different currents that guide us to the schools of feeding fish. (MacGillivray 1995)
Our study of tides here has two aims: (1) to help you better appreciate the importance of tides for human activities; and (2) to help you better understand discussions about changes in sea level. We’re especially concerned about sea level rise—caused by global warming—which already affects coastal cities around the world. Will your favorite seaside hangout be affected? Let’s find out.