What caused the world’s largest die-off of mangroves? A wobble in the moon’s orbit is partly to blame

Posted: September 16, 2022 by oldbrew in climate, Cycles, ENSO, moon, Natural Variation, research, sea levels, Tides

2015 Gulf of Carpentaria mangrove die-off, from space [image credit: NASA]


Even the type of local tides was involved. Researchers conclude: we can chalk the 2015 mass death up to “natural causes.”
– – –
Over the summer of 2015, 40 million mangroves died of thirst, says Phys.org.

This vast die-off—the world’s largest ever recorded—killed off rich mangrove forests along fully 1,000 kilometers of coastline on Australia’s Gulf of Carpentaria.

The question is, why? Last month, scientists found a culprit: a strong El Niño event, which led to a temporary fall in sea level.

That left mangroves, which rely on tides covering their roots, high and dry during an unusually dry early monsoon season.

Case closed. Or is it?

While evidence clearly implicates El Niño, we found this climate cycle had a very large accomplice: the moon.

In our study, published in Science Advances today, we mapped the expansion and contraction of mangrove forest cover over the past 40 years, and found clear evidence that the moon’s orbital wobble had an effect.

Our mapping also shows mangroves are expanding and their canopy thickening across the entire continent, which is most likely due to higher carbon dioxide levels. Spectacular though it was, the Gulf of Carpentaria mangrove dieback event was entirely natural.

What clues gave away the moon’s role?

During El Niño cycles like the one in 2015, sea levels fall around Australia and other countries in the western Pacific.

But these climate cycles affect the whole Indo-Australian region. If El Niño was the main cause, mangroves elsewhere should have been hit too. But the deaths of these tidal-flat dwelling shrubs and trees were largely localized to the Gulf of Carpentaria.

Death rates were highest along shorelines that experience the full range of the tide. By contrast, mangroves continued to thrive at the tidal limits of the estuaries, far into the floodplains where climatic effects ought to be most strongly felt.

That’s where the moon comes in—and particularly the “lunar wobble.” Back in 1728, astronomers noticed the plane in which the moon orbits Earth isn’t fixed. Instead, it wobbles up and down, a bit like a spinning coin as it begins to slow.

When we mapped the extent and distribution of Australian mangrove forests over the past 40 years, we found clear signs of the moon’s wobble at work. This 18.6-year orbital cycle turns out to be the main reason why mangrove canopy expands and contracts around most of Australia’s coastlines—and explains the patterns of mangrove mortality in the Gulf of Carpentaria.

You might be wondering why the wobble has such influence over whether mangroves live or die. It’s the tides. The wobble changes how the moon’s gravity pulls on the world’s oceans, so periods of exceptionally high tides are followed by exceptionally low tides 9.3 years later.
. . .
We now know short-term natural climate cycles like El Niño likely cannot cause widespread mangrove deaths by themselves. And we can anticipate the danger times when it coincides with the low tides brought by the lunar wobble.

While mangroves still face an uncertain future adapting to a world of higher seas, we can chalk the 2015 mass death up to “natural causes.”

Full article here.

Comments
  1. […] What caused the world’s largest die-off of mangroves? A wobble in the moon’s orbit is partly to … […]

  2. […] Further Reading about the Mangrove dieback can be had on Tallbloke’s TalkShop. […]

  3. Saighdear says:

    a temporary fall in sea level. – or a regular occurrence? Anyroad, there are tide tables for mariners, Farmer’s Almanac for others, but for me, Moonrise & fall is one thing, but WHERE is the moon in the sky on a particular night? we had full moon for a very short period , past fewdays ( v low in sky) and last night 1/2 ( nay Zero point Four Nine of a moon) almost overhead. Question: what tables would tell me where the moon is at Moonrise & Set and how high in the sky will it be? We’ve had full moons on clear summer skies which were pitch black ( no full moon to be seen for very long ). I can then deduce what kind of tide I may see on the tidal pastures.

  4. […] What caused the world’s largest die-off of mangroves? A wobble in the moon’s orbit is partly to … […]

  5. oldbrew says:

    The local conditions (from the full blog post article)…

    The Gulf of Carpentaria is one of the few coastlines in Australia with diurnal tides. Most other coastlines have two high tides each day. Put together, this meant that in 2015, semi-diurnal coastlines had bigger-than-usual tides, while rare diurnal coastlines like those along the gulf had smaller-than-usual tides.

    This explains why mangroves in the semi-diurnal coastlines directly next to the Gulf of Carpentaria were spared over the 2015–16 summer.

  6. P.A.Semi says:

    re Saighdear “WHERE is the moon in the sky on a particular night?”

    Generally speaking – summer full-moons are low, winter full-moons are high, because Moon is just 5° from ecliptic, so close to the plane where Sun is… Full-moon is directly opposite to Sun, so it rises around 6pm, and every day it is by some 50 minutes later than previous day (24/29*60), so that C moon rises later in night, while D moon rises before sunset… Most high full-moon is 23.5+5 = 28.5° above equator, so at 50° N latitude it is at most 68.5° above horizon or 21.5° from zenith. Moon has 0.5° in diameter, so at 50° N latitude it is 43 moon diameters from zenith at highest winter full-moon…

    Then, particularly, it is interesting, whether the moon is currently in rising or descending phase, when is high-moon and low-moon, which does not coincide with full-moon or new-moon, as this high/low moon has effect on plant growth, as pointed out and proved by Maria Thun and her calendar, which is now published by her son Matthias K. Thun yearly…
    I know where to buy the Czech version of her calendar
    https://pro-bio.cz/publikace/vysevni-dny-podle-marie-thunove-2022/
    but not sure where to find English version or German original…

    πα½

  7. P.A.Semi says:

    As there is raging Energy Crisis since late 2021 chiefly caused by Green Deal Fanatics and Corporate Banksters to dig high profits chiefly from European citizens,
    it is interesting, whether the next winter will be cold or warm…

    Unfortunately, it can be expected, that the following winter 2022-23 will be colder, than previous winters:

    The Earth orbits the Sun on an ellipse, near at northern winter, far at northern summer, which softens both northern winters (not that cold as southern) and summers (not that warm as southern)…
    Overall in Milankovich cycle, the Earth orbit is approaching circle, so in next ten thousand years, it will be more and more circular and this climate softening effect will diminish…
    And year beside year it slightly differs, whether it is more circular or more elliptic, by little… But I found, that it may be linked to yearly differences in average winter temperature over Europe (and probably USA too?)…
    Last time I’ve posted here a similar picture, the temperature record was “poisoned” by using global average temperature from NOAA/NCEP reanalysis, which has spoiled polar regions, so now it’s only Europe from that dataset and the match seems to be quite well…

    On the chart, black line is EMB perihelium distance in January inverted, high is near Sun, low is more far from Sun, and blue line is average temperature over Europe in February at 850hPa level… Next few winters can be expected little colder than previous three years… (perihelium is closer to Sun, when Jupiter in January is near the Sun)
    (Using EMB Earth Moon Barycenter instead of Earth avoids “noise” due to full-moon new-moon difference at the time of perihelium, but as fm/nm is just a 2x fortnight cycle, but the EMB perihelium distance differs for whole December/January… or should I use Earth instead of EMB and then integrate it over whole winter?)

    πα½

  8. Chaswarnertoo says:

    Are we sure it’s not the ‘green’ tidal power projects wobbling the moon and causing the mangrove climate disaster…..😇

  9. Phoenix44 says:

    So the original study was on a tiny fraction of the population and the rest of the population was in good health…but climate change.

    Absolute deliberate fraud.

  10. Chaeremon says:

    The tides, not performing their “average / normal” heat exchange between sea and land due to the wobble, can be cause of change in sea temperatures.

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