Scientists have long assumed that Antarctic ice sheets are essentially

Question

Scientists have long assumed that Antarctic ice sheets are essentially stable. In theory, snowfall replenishes ice sheets, replacing the mass lost when ice from the sheets flows outward in solid streams and sheds into the ocean as icebergs. However, satellite measurements show that the West Antarctic ice sheet has been losing mass and that its ice streams are accelerating.

To explain these changes, geophysicist Robin Bell and her colleagues have been studying the role played by liquid water under the ice sheet. They have found that although the base of the ice sheet is insulated from changing atmospheric temperatures, it can melt because of friction as it moves over underlying rock. The meltwater lubricates and accelerates the ice streams. Furthermore, some lakes below the ice sheets are draining, adding more lubrication that further destabilizes the streams.

Ordinarily, ice streams cause ice shelves to accumulate at the streams’ ocean outlets. These shelves block and slow the streams. But since ice shelves are sensitive to ocean temperatures, global warming can melt them. In 2002, ice streams flowing into the Larsen B ice shelf in West Antarctica accelerated dramatically after much of the shelf collapsed into the ocean. This suggests that global warming could allow far more land-based ice to flow into the ocean, raising sea levels rapidly.   1 
1. The passage most strongly suggests that some ice streams have accelerated because
A. ocean temperatures have increased
B. the West Antarctic ice sheet has lost mass
C. global warming has reduced Antarctic snowfall
D. heat from friction indirectly caused an ice shelf to collapse
E. meltwater has been creating numerous new lakes beneath the ice sheets

2 
2. The passage most clearly indicates that some liquid water below the ice sheets

A. originally entered lakes that are under the ice sheets because of melting resulting from increasing atmospheric temperatures
B. is creating new ice streams
C. replaces lost mass in ice shelves
D. has increased the frictional resistance between ice sheets and the underlying rock
E. is flowing out of lakes that are under the ice sheets

3 
3. In the context of the passage, the main function of the first paragraph is to

A. account for observations that appear to conflict with a widely held scientific theory
B. state a hypothesis for which the subsequent paragraphs provide theoretical and observational support
C. describe a discrepancy between theory and observations that is explained in the subsequent paragraphs
D. present evidence to support a conclusion stated in the following paragraph
E. summarize the premises of an argument that the rest of the passage develops in greater detail

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cosmic_matters1 · Accepted Answer

A. Originally entered...temperatures. 
well the option is no where mentioned in the para and is kind of vague. 
B. is creating new ice streams.
It is said to have accelerated the flow of the streams, but no where to create new streams. 
C. replaces lost mass in ice shelves.
 Well it lubricates, not form ice mass.
D.has increased the frictional resistance. Absolutely not, the paragraph has mentioned the opposite actually, i.e,
 
E.  is flowing out of lakes that are under the ice sheets
Well yes, mentioned here, take a look.
 
That's it, if you like it, hit the kudos button.

purplelemonsoda · Answer

1.
   important to read the whole question  completely . "The passage most strongly suggests that  some  ice streams have accelerated because"

We're looking for a REASON for the acceleration of SOME ice streams. so to rephrase the question: WHY ARE ICE STREAMS ACCELERATING?

Let's find a reason that explains the reason they're accelerating.

A. The passage notes that ocean temperatures can melt ice shelves, which normally act as a barrier to slow down ice streams. 
When ice shelves melt or collapse, as in the case of the Larsen B ice shelf, the ice streams that flow into them accelerate dramatically. 
This indicates that increased ocean temperatures contribute to the acceleration of ice streams by weakening or removing the ice shelves. 
(TRAP) B. the West Antarctic ice sheet has lost mass: This is a result of the ice stream acceleration, not its cause. The cause is explained in the second instance of West Antarctic. 
C. global warming has reduced Antarctic snowfall: The passage does not mention reduced snowfall as a cause of the changes in ice streams.
D. heat from friction indirectly caused an ice shelf to collapse: While friction does cause meltwater, the passage attributes ice shelf collapse directly to ocean temperature changes, not friction.
E. meltwater has been creating numerous new lakes beneath the ice sheets: While meltwater contributes to ice stream lubrication, the acceleration of some ice streams (like those connected to the Larsen B ice shelf) is directly linked to the loss of ice shelves due to increased ocean temperatures.

3. I think most of us would agree the debate is between A and C.

So let's zoom into the key Points in the answer choice A:
1) The widely held scientific theory: Antarctic ice sheets are stable due to snowfall replenishment.
2) The conflicting observation: Satellite measurements show mass loss in the West Antarctic ice sheet and accelerated ice streams.

Why A is not correct: 
"Account for" implies resolving or explaining the conflict. The first paragraph introduces the conflict (between the stable ice sheet theory and satellite observations), but it does not account for or resolve it.
The explanation for the observed ice sheet behavior is provided in the subsequent paragraphs, which describe the role of meltwater and global warming. Therefore, the first paragraph does not fulfill the function of explaining or "accounting for" the observations.
 Why C is correct: 
The phrase "describe a discrepancy" aligns with what the first paragraph does: it highlights the conflict between the theory of stability and the observed ice sheet mass loss and acceleration.
This discrepancy is explained in detail in the following paragraphs, which discuss frictional melting, subglacial lakes, and ice shelf collapse.
 Difference Between A and C: 
A suggests the first paragraph provides a resolution or explanation (it doesn’t).
C correctly identifies that the first paragraph describes the conflict, leaving the explanation to the rest of the passage.
 How to think about this: 
If the first paragraph explained why the theory is wrong or how the observations fit within the theory, A would be correct. However, since it only sets up the problem (the discrepancy), C is the better choice.

pulkitrana · Answer

Quest 1 
It is nowhere mentioned that oceans temperature has increased.
D looks like a much better answer choice. 
Experts pls help. Thanks  GMATNinja   KarishmaB   egmat

dazzler97 · Answer

Pl refer to 3rd paragraph . The line - "But since ice shelves are sensitive to ocean temperatures, global warming can melt them."
This means the ocean temperatures are increasing => ice shelves are compromised.

Jayam12 · Answer

Can someone explain how to eliminate option A in Q3?

Sajjad1994 · Answer

The main function of the first paragraph in the passage is to set up the context and introduce the apparent discrepancy between long-standing scientific assumptions and recent observations regarding the stability of Antarctic ice sheets.

A  is incorrect because the first paragraph doesn't directly account for the observations. Instead, it sets up the background by stating the long-held assumption and introduces the observed changes, leaving the explanation for subsequent paragraphs.

adityakaregamba · Answer

can someone explain Q2 please ?

utkarsh27 · Answer

1. The passage most strongly suggests that some ice streams have accelerated because
A. ocean temperatures have increased
B. the West Antarctic ice sheet has lost mass
C. global warming has reduced Antarctic snowfall
D. heat from friction indirectly caused an ice shelf to collapse
E. meltwater has been creating numerous new lakes beneath the ice sheets

Writing down my understanding. I couldn't decide between A and B properly. I chose B initially. Can someone point why B might be wrong?

a - ocean temperatures have increased - Refer lines: "But since ice shelves are sensitive to ocean temperatures, global warming can melt them. In 2002, ice streams flowing into the Larsen B ice shelf in West Antarctica accelerated dramatically after much of the shelf collapsed into the ocean."
Indicates ice streams accelerated because ice shelf collapsed reducing blockage that used to be faced by ice streams. And ice shelf collapsed due to increasing ocean temperatures.

b - the West Antarctic ice sheet has lost mass -
for B: even though specific about Western Antarctic sheet it does provide reason for atleast "some" ice streams accelerating. Also ice sheet as per passage collapsed which is kind of equivalent to losing mass. So if ice sheet is reduced, it should provide less blockage for ice streams, hence looks like valid reason for accelreating ice streams.
against B: is very specifically only about West Antarctic ice sheet? in General rising ocean temperatures is probably more apt reason for indirectly accelerating ice streams? Also the ice shelf collapsed instead of losing mass is probably not exactly correct?

c - global warming has reduced Antarctic snowfall - while this might be true it has not been mentioned anywhere about reduction in snowfall.

d - heat from friction indirectly caused an ice shelf to collapse - heat from friction causes base of ice sheet to melt. but nowhere mentioned that it also causes collapse of ice shelf.

e - meltwater has been creating numerous new lakes beneath the ice sheets - Not mentioned in passage that meltwater is creating lakes beneath ice sheets. So this reason factually looks wrong.

sayan640 · Answer

KarishmaB   MartyMurray  I also have similar doubt about question A . Can you please explain question 1 ? I think D should be the answer.  chetan2u

hellothere1234 · Answer

It says, Ordinarily ice streams cause ice shelves to accumulate at the streams ocean outlers, these shelves block and slow the streams, but since the shelves are sensitive to ocean temperatures, global warming can melt them. ... Lasrsen B.. acc dramatically after shelf collapsed into the ocean

So a. Ocean temp have increased

So a. Ocean temp have increased

sanebeyondone · Answer

I think there is a trick of word paraphrasing here right?
I wasn't sure that "liquid water under the ice sheet" is same with (=) "some lakes below the ice sheets" or not.

MalachiKeti · Answer

MartyMurray   GMATNinja  can you help with Q 2

Vitthal19 · Answer

but in option 3 the answer starts with DESCRIBE but the 1st paragraph is just introducing or just stating the contradiction so I thought that this option should be eliminated on the word DESCRIBE.

maskedmello · Answer

F...i missed the "first" and went on with A.

Scientists have long assumed that Antarctic ice sheets are essentially

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Scientists have long assumed that Antarctic ice sheets are essentially

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