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# Recent studies of sediment in the North Atlantic’deep

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Recent studies of sediment in the North Atlantic’deep  [#permalink]

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05 May 2018, 09:49
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Recent studies of sediment in the North Atlantic’deep waters reveal possible cyclical patterns in the history of Earth’s climate. The rock fragments in these sediments are too large to have been transported there by ocean currents, they must have reached their present locations by traveling in large icebergs that floated long distance from their point of origin before melting. Geologist Gerard Bond noticed that some of the sediment grains were stained with iron oxide, evidence that they originated in locales where glaciers had overrun outcrops of red sandstone. Bond’s detailed analysis of deep-water sediment cores showed changes in the mix of sediment sources over time: the proportion of these red-stained grains fluctuated back and forth from lows of 5 percent to highs of about 17 percent, and these fluctuations occurred in a nearly regular 1,500-year cycle.

Bond hypothesized that the alternation cycles might be evidence of changes in ocean-water circulation and therefore in Earth’s climate. He knew that the sources of the red-stained grains were generally closer to the North Pole than were the places yielding a high proportion of“clean” grains. At certain times, apparently, more icebergs from the Arctic Ocean in the far north were traveling south well into the North Atlantic before melting and shedding their sediment.

Ocean waters are constantly moving. And water temperature is both a cause and an effect of this movement. As water cools, it becomes denser and sinks to the ocean’s bottom. During some periods, the bottom layer of the world’s oceans comes from cold, dense water sinking in the far North Atlantic. This causes the warm surface waters of the Gulf Stream to be pulled northward. Bond realized that during such periods, the influx of these warm surface waters into northern regions could cause a large proportion of the icebergs that bear red grains to melt before traveling very far into the North Atlantic. But sometimes the ocean’s dynamic changes, and waters from the Gulf stream do not travel northward in this way. During these periods, surface waters in the North Atlantic would generally be colder, permitting icebergs bearing red-stained grains to travel farther south in the North Atlantic before melting and depositing their sediment.

The onset of the so-called Little Ice Age(1300-1860), which followed the Medieval Warm Period of the eighth through tenth centuries, may represent the most recent time that the ocean’s dynamic changed in this way. If ongoing climate-history studies support Bond’s hypothesis of 1,500-year cycles, scientists may establish a major natural rhythm in Earth’s temperatures that could then be extrapolated into the future. Because the midpoint of the Medieval Warm Period was about AD.850, an extension of Bond’s cycles would place the midpoint of the next warm interval in the twenty-fourth century.
According to the passage, which of the following is true of the rock fragments contained in the sediments studied by Bond?

A) the majority of them are composed of red sandstone.
B) they must have reached their present location over 1,500 years ago.
C) they were carried by icebergs to their present location.
D) Most of them were carried to their present location during a warm period in Earth’s climatic history.
E) They are unlikely to have been carried to their present location during the Little Ice Age.

Spoiler: :: OA
C

In the final paragraph of the passage, the author is concerned primarily with

B) pointing out a potential flaw in Bond’s hypothesis
C) suggesting a new focus for the study of ocean sediments
D) tracing the general history of Earth’s climate
E) discussing possible implications of Bond’s hypothesis.

Spoiler: :: OA
E

According to the passage, Bond hypothesized that which of the following circumstances would allow red-stained sediment grains to reach more southerly latitudes?

A) Warm waters being pulled northward from the Gulf Stream
B) Climatic conditions causing icebergs to melt relatively quickly
C) Icebergs containing a higher proportion of iron oxide than usual
D) The formation of more icebergs than usual in the far north
E) the presence of cold surface waters in the North Atlantic

Spoiler: :: OA
E

It can be inferred from the passage that in sediment cores from the North Atlantic’s deep waters, the portions that correspond to the Little Ice Age

A) differ very little in composition from the portions that correspond to the Medieval Warm Period.
B) fluctuate significantly in composition between the portions corresponding to the 1300s and the portions corresponding to the 1700s
C) would be likely to contain a proportion of red-stained grains closer to 17 percent than to 5 percent.
D) show a much higher proportion of red-stained grains in cores extracted from the far north of the North Atlantic than in cores extracted from further south
E) were formed in part as a result of Gulf Stream waters having been pulled northward

Spoiler: :: OA
C

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Re: Recent studies of sediment in the North Atlantic’deep  [#permalink]

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31 Aug 2018, 20:25
2
+1 kudos to all the posts containing proper explanations for all questions
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Re: Recent studies of sediment in the North Atlantic’deep  [#permalink]

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31 Aug 2018, 23:04
@workaut please guide on question 4, thanks
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Re: Recent studies of sediment in the North Atlantic’deep  [#permalink]

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01 Sep 2018, 02:41
4
warm Medieval period was followed by little ice age, which means surface water was cold. Therefore, ice bergs would have retained more of red sediments as they would not have melted .And as mentioned that the red content in these sediments were form 5 to 17 ,further, was brought only by water from north .Finally,in little ice age ice bergs would have carried the maximum red pigment .Ans C
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Re: Recent studies of sediment in the North Atlantic’deep  [#permalink]

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01 Sep 2018, 05:57
Couldn't get the answer for the 4th question. Can anyone explain how did you reach answer C? Please give evidence from the passage if possible.

Thanks,
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Re: Recent studies of sediment in the North Atlantic’deep  [#permalink]

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01 Sep 2018, 06:32
carcass

Why can't D be the answer to Q4?
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Re: Recent studies of sediment in the North Atlantic’deep  [#permalink]

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01 Sep 2018, 08:30
Top Contributor
Honestly, I really do not know where you inferred D from the passage.

Please, show me a possible connection or portion of the passage in which you can see that D is a possible answer.

Thank you
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Re: Recent studies of sediment in the North Atlantic’deep  [#permalink]

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01 Sep 2018, 22:52
1
2
carcass wrote:
Recent studies of sediment in the North Atlantic’deep waters reveal possible cyclical patterns in the history of Earth’s climate. The rock fragments in these sediments are too large to have been transported there by ocean currents, they must have reached their present locations by traveling in large icebergs that floated long distance from their point of origin before melting. Geologist Gerard Bond noticed that some of the sediment grains were stained with iron oxide, evidence that they originated in locales where glaciers had overrun outcrops of red sandstone. Bond’s detailed analysis of deep-water sediment cores showed changes in the mix of sediment sources over time: the proportion of these red-stained grains fluctuated back and forth from lows of 5 percent to highs of about 17 percent, and these fluctuations occurred in a nearly regular 1,500-year cycle.

Bond hypothesized that the alternation cycles might be evidence of changes in ocean-water circulation and therefore in Earth’s climate. He knew that the sources of the red-stained grains were generally closer to the North Pole than were the places yielding a high proportion of“clean” grains. At certain times, apparently, more icebergs from the Arctic Ocean in the far north were traveling south well into the North Atlantic before melting and shedding their sediment.

Ocean waters are constantly moving. And water temperature is both a cause and an effect of this movement. As water cools, it becomes denser and sinks to the ocean’s bottom. During some periods, the bottom layer of the world’s oceans comes from cold, dense water sinking in the far North Atlantic. This causes the warm surface waters of the Gulf Stream to be pulled northward. Bond realized that during such periods, the influx of these warm surface waters into northern regions could cause a large proportion of the icebergs that bear red grains to melt before traveling very far into the North Atlantic. But sometimes the ocean’s dynamic changes, and waters from the Gulf stream do not travel northward in this way. During these periods, surface waters in the North Atlantic would generally be colder, permitting icebergs bearing red-stained grains to travel farther south in the North Atlantic before melting and depositing their sediment.

The onset of the so-called Little Ice Age(1300-1860), which followed the Medieval Warm Period of the eighth through tenth centuries, may represent the most recent time that the ocean’s dynamic changed in this way. If ongoing climate-history studies support Bond’s hypothesis of 1,500-year cycles, scientists may establish a major natural rhythm in Earth’s temperatures that could then be extrapolated into the future. Because the midpoint of the Medieval Warm Period was about AD.850, an extension of Bond’s cycles would place the midpoint of the next warm interval in the twenty-fourth century.
According to the passage, which of the following is true of the rock fragments contained in the sediments studied by Bond?

A) the majority of them are composed of red sandstone.
B) they must have reached their present location over 1,500 years ago.
C) they were carried by icebergs to their present location.
D) Most of them were carried to their present location during a warm period in Earth’s climatic history.
E) They are unlikely to have been carried to their present location during the Little Ice Age.

Spoiler: :: OA
C

In the final paragraph of the passage, the author is concerned primarily with

B) pointing out a potential flaw in Bond’s hypothesis
C) suggesting a new focus for the study of ocean sediments
D) tracing the general history of Earth’s climate
E) discussing possible implications of Bond’s hypothesis.

Spoiler: :: OA
E

According to the passage, Bond hypothesized that which of the following circumstances would allow red-stained sediment grains to reach more southerly latitudes?

A) Warm waters being pulled northward from the Gulf Stream
B) Climatic conditions causing icebergs to melt relatively quickly
C) Icebergs containing a higher proportion of iron oxide than usual
D) The formation of more icebergs than usual in the far north
E) the presence of cold surface waters in the North Atlantic

Spoiler: :: OA
E

It can be inferred from the passage that in sediment cores from the North Atlantic’s deep waters, the portions that correspond to the Little Ice Age

A) differ very little in composition from the portions that correspond to the Medieval Warm Period.
B) fluctuate significantly in composition between the portions corresponding to the 1300s and the portions corresponding to the 1700s
C) would be likely to contain a proportion of red-stained grains closer to 17 percent than to 5 percent.
D) show a much higher proportion of red-stained grains in cores extracted from the far north of the North Atlantic than in cores extracted from further south
E) were formed in part as a result of Gulf Stream waters having been pulled northward

Spoiler: :: OA
C

Passage structure:
1. GBond:New Study(determine CP of earth's Climate). edivence: sediments with diff conc of red stone(5 to 17 %) cycled 1500 yr.
2. hyp: alternate cycle>>(ocean wtr circulation)>>earth climate. expalins the process. cold temp(dense water sinks down from NA >> warm GS water pulled northward>>icebergs with red sediments melt(imp b4 travelling far north). BUT ocean water dynamic change>>iceberg travel south. [this is how change in conc of sediments 5 to 17 %].
3. implication of the hyp: recent climatic condtn. Ice age> medival(warm age)- ++ hypothesis. Scientists can get help from the stads to continue study.

prethinking:
main idea and Tone: Author introduces a new study>>explains a hyp with process and facts>>implications
so, descriptive and supportive.

1. according to question(one word elimination and directly stated)
A. composed of ...(OUT passage stated that conc varying 5 to 17 %)
B.must have (might be true as its a hypothesis , strong word,OUT)
C. 2 line of first para, The rock fragments .... melting. Keep IT.
D. OPPOSITE , OUT
E. not stated directly, OUT

2. our pre thinking : implications or future research.. E (Correct)

3. point 2 statement of passage structure( BUT ocean water dynamic change>>iceberg travel south ..)
North Atlantic would generally be colder,........

4. Inference type:
question states that, little ice age >> medieval period means change in the flow along with the change in the conc : from the ..the proportion of these red-stained grains fluctuated back and forth from lows of 5 percent to highs of about 17 percent, and these fluctuations occurred in a nearly regular 1,500-year cycle.
A. concerned about the correlation btw north Atlantic water and the Ice Age...OUT
B. cannot directly infer about the ages 1300 and 1700 cause, ocean water dynamic changes alternate the behavior, which can happen during the periods.. so not evident.OUT
C. yes as per the thinking. Keep it and looking for the better option.
D. third para implies that some times even large conc of red sediments traveled to the SOUTH due to the dynamic changes.
E. OOS. dont know which formed what. OUT
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Re: Recent studies of sediment in the North Atlantic’deep  [#permalink]

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02 Sep 2018, 20:01
1
8 minutes ( all correct )
1. The passage states " The rock fragments in these sediments are too large to have been transported there by ocean currents, they must have reached their present locations by traveling in large icebergs that floated long distance from their point of origin before melting "
This makes it clear that option C is correct

2. The passage states " If ongoing climate-history studies support Bond’s hypothesis of 1,500-year cycles, scientists may establish a major natural rhythm in Earth’s temperatures that could then be extrapolated into the future"
Thus we can infer that in the last paragraph the author is trying to explain the possible implications of Mr. Bond's theory. Hence E

3. The passage states " But sometimes the ocean’s dynamic changes, and waters from the Gulf stream do not travel northward in this way. During these periods, surface waters in the North Atlantic would generally be colder"
Here the author explains a second case scenario when large proportion of the icebergs that bear red grains to melt before traveling very far into the South Atlantic and not the North Atlantic.
Hence E

4. "Little ICE AGE " talks about a second case scenario (as discussed in 3) hence eliminate D and E
The passage states
A. "sediment cores showed changes in the mix of sediment sources over time: the proportion of these red-stained grains fluctuated back and forth from lows of 5 percent to highs of about 17 percent, and these fluctuations occurred in a nearly regular 1,500-year cycle."
B. The onset of the so-called Little Ice Age(1300-1860), which followed the Medieval Warm Period of the eighth through tenth centuries, may represent the most recent time that the ocean’s dynamic changed in this way.
So taking into consideration present times (which is the next cycle) we can infer that the glaciers would have melted in the south Atlantic and the highest concentration would have been around North for the previous cycle as during the Litlle Ice age the glaciers moved towards south altitude.
Hence C
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Re: Recent studies of sediment in the North Atlantic’deep  [#permalink]

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04 Sep 2018, 18:22
Doubt on option B question 4

fluctuate significantly in composition between the portions corresponding to the 1300s and the portions corresponding to the 1700s

since, it is end of Medieval Warm Period, it is expected the percentage to be less in start of 1300s but around 1700s, it is expected to be high in composition. then why option B is incorrect?

because of fluctuate?. It wont fluctuate significantly rather it will be steep rise from 1300 to 1700!!

Regards
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Re: Recent studies of sediment in the North Atlantic’deep  [#permalink]

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04 Sep 2018, 18:27
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Re: Recent studies of sediment in the North Atlantic’deep  [#permalink]

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06 Sep 2018, 10:18
2
Prateek176 wrote:
carcass

Why can't D be the answer to Q4?

It can be inferred from the passage that in sediment cores from the North Atlantic’s deep waters, the portions that correspond to the Little Ice Age

A) differ very little in composition from the portions that correspond to the Medieval Warm Period.
B) fluctuate significantly in composition between the portions corresponding to the 1300s and the portions corresponding to the 1700s
C) would be likely to contain a proportion of red-stained grains closer to 17 percent than to 5 percent.
D) show a much higher proportion of red-stained grains in cores extracted from the far north of the North Atlantic than in cores extracted from further south
E) were formed in part as a result of Gulf Stream waters having been pulled northward

Nice that you were able to eliminate A,B and E.Now between D and C(correct answer).if D was to be correct which says that the North cores have higher proportione it means that the iceburgs were melted in the north itself and never reached down south. But we know from the passage that it was an ice age that measn colder tempratures. and due to that the iceburgs did not melt in the north but travelled down south.

So D is out.

Now why C is correct is because if it is ice age it is more likely that higher proportions of iceburgs travelled south that means higher concentration of red stained grains reached south.

I hope is was clear in explaining.
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Re: Recent studies of sediment in the North Atlantic’deep  [#permalink]

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26 Oct 2018, 08:03
Nice passage I answered 4 Question wrong, was a hard one for me
Re: Recent studies of sediment in the North Atlantic’deep   [#permalink] 26 Oct 2018, 08:03
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